UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS 

COLLEGE  OF  AGRICULTURE 
AGRICULTURAL  EXPERIMENT  STATION 

Berkeley,  California 


Red  Spiders  and  Mites  of  Citrus  Trees 


BY 


H.  J.  QUAYLE 


BULLETIN  234 

BERKELEY,  CAL.,  NOVEMBER,  1912 


Friend  Wm.  Richardson,  Superintendent  op  State  Printing 
sacramento,,  california 

19  12 


Benjamin  Ide  AYheeler,  President  of  the  University. 

EXPERIMENT    STATION    STAFF. 

Thos.   Forsyth  Hunt,  D.Agr.,   Director. 
E.  J.  Wickson,  M.A.,  Horticulturist. 

E.  W.  Hilgard,  Ph.D.,  LL.D.  Chemist   (Emeritus). 
W.  A.  Setchell,  Ph.D.,  Botanist. 

Leroy  Anderson,  Ph.D.,  Dairy  Industry. 

M.  E.  Jaffa,  M.S.,  Nutrition  Expert. 

R.  H.  Loughridge,  Ph.D.,  Soil  Chemist  and  Physicist   (Emeritus). 

C.  W.  Woodworth,  M.S.,  Entomologist. 

Ralph  E.   Smith,  B.S.,   Plant  Pathologist  and  Superintendent  of  Southern  California 

Pathological  Laboratory  and  Experiment  Station. 
J.  E.  Coit,  Ph.D.,  Citriculturist. 
P.  R.  Marshall,  B.S.A.,  Animal  Industry. 
H.  J.  Webber,  Ph.D.,  Director  Citrus  Experiment  Station,  Riverside. 

A.  V.  Stubenrauch,  M.S.,  Pomologist. 
C.  F.  Shaw,  B.S.,  Soil  Technologist. 

J.  W.  Gregg,  B.S.,  Floriculturist. 
J.  W.  Gilmore,  M.S. A.,  Agronomist. 

G.    W.    Shaw,  M.A.,    Ph.D.,    Experimental   Agronomist   and  Agricultural    Technologist, 
in  charge  of  Cereal  Stations. 

B.  A.  Etcheverry,  B.S.,  Irrigation  Expert. 

F.  T.  Bioletti,  M.S.,  Viticulturist. 

W.  T.  Clark,  B.S.,  Assistant  Horticulturist  and  Superintendent  of  University  Exten- 
sion in  Agriculture. 
John  S.  Burd,  B.S.,  Chemist,  in  charge  of  Fertilizer  Control. 

C.  B.  Lipman,  Ph.D.,  Soil  Chemist  and  Bacteriologist. 

George    E.    Colby,    M.S..    Chemist    (Fruits,    Waters,    and   Insecticides),    in    charge    of 

Chemical  Laboratory. 
H.  J.  Quayle,  M.S.,  Assistant  Entomologist. 
H.  M.  Hall,  Ph.D.,  Assistant  Botanist. 
C.  M.  Haring,  D.V.M.,  Veterinarian  and  Bacteriologist. 

E.  B.  Babcock,  B.S.,  Agricultural  Education.  ' 

W.  B.  Herms,  M.A.,  Assistant  Entomologist. 
W.  B.  Horne,  B.S.,  Assistant  Plant  Pathologist. 
L.  M.  Davis,  B.S.,  Assistant  Dairy  Industry. 
W.  W.  Bonns,  M.S.,  Assistant  Pomologist. 

A.  J.  Gaumnitz,  M.S.,  Assistant  Agronomist,  University  Farm,  Davis. 
T.  F.  Hunt,  B.S.,  Assistant  Plant  Pathologist. 

E.  H.  Hagemann,  Assistant  in  Dairying,  Davis. 

J.  I.  Thompson,  B.S.,  Assistant  Animal  Industry,  Davis. 
J.  C.  Bridwell,  B.S.,  Assistant  Entomologist. 
L.  Bonnet,  LA.,  Assistant  Viticulturist. 

F.  C.  H.  Flossfeder,  Assistant  in  Viticulture,  University  Farm,  Davis. 
P.  L.  Hibbard.  B.S.,  Assistant  Fertilizer  Control  Laboratory. 

C.  H.  McCharles,  M.S.,  Assistant  Agricultural  Chemical  Laboratory. 

B.  A.  Madson,  B.S.A.,  Assistant  Experimental  Agronomist. 

Walter  E.  Packard,   M.S.,  Field  Assistant  Imperial  Valley  Investigation,  El  Centre 
S.   S.   Rogers,   B.S.,  Assistant  Plant  Pathologist,   Plant  Disease  Laboratory,   Whittier. 

C.  O.  Smith,  M.S.,  Assistant  Plant  Pathologist,  Plant  Disease  Laboratory,  Whittier. 

E.  H.  Smith,  M.S.,  Assistant  Plant  Pathologist. 

C.  L.  Roadhouse,  D.V.M.,  Assistant  in  Veterinary  Science. 

F.  M.  Hayes,  D.V.M..  Assistant  Veterinarian. 
P.  S.  Burgess,  M.S.,  Assistant  Soil  Chemist. 
W.  F.  Gericke,  B.S.,  Assistant  Soil  Chemist. 

M.  E.  Stover,  B.S.,  Assistant  in  Agricultural  Chemical  Laboratory. 
W.  H.  Volck,  Field  Assistant  in  Entomology,  Watsonville. 
E.  L.  Morris,  Field  Assistant  in  Entomology,  San  Jose. 

E.  E.  Thomas,  B.S.,  Assistant  Chemist,  Plant  Disease  Laboratory,  Whittier. 
A.  B.   Shaw,  B.S.,  Assistant  in  Entomology. 

G.  P.  Gray,  M.S.,  Chemist  in  Insecticides. 

H.   D.    Young,   B.S.,   Assistant   in   Agricultural   Chemistry,    Plant   Disease   Laboratory, 

Whittier. 
A.  R.  Tylor,  B.S.,  Assistant  in  Plant  Pathology,  Plant  Disease  Laboratory,  Whittier. 
W.  V.  Cruess,  B.S.,  Assistant  in  Zymology. 

J.    F.   Mitchell,  D.V.M.,   Assistant   in  Veterinary   Laboratory. 
M.  R.  Miller,  B.S.,  Assistant  Chemist  in  Insecticides. 

F.  H.  Wilson,  B.S.,  Assistant  in  Soil  Chemistry. 
W.  M.  Mertz,  Assistant  in  Pomology,  Riverside. 

C.  R.  George,  B.S.,  Assistant  in  Animal  Industry. 

Anna  M.  Lute,  A.B.,  Scientific  Assistant,  U.  S.  Dept.  of  Agriculture. 

D.  L.  Bunnell,  Secretary  to  Director. 


CONTENTS. 


Tagc. 

Introduction    483 

Nature  of  Injury , 483 

Species  Concerned 485 

The  Citrus  Red  Spider   (Tctranychus  mytilaspidis  Riley) 487 

Early  Account 487 

Nature  of  Injury 487 

Distribution    487 

Life  History  and  Habits 488 

The   Egg  488 

Appearance 488 

Number 489 

Proportion  Hatching 489 

Period  of  Incubation 489 

The  Young 489 

Appearance  and  Emergence 489 

Process  of  Molting 490 

The  Adult 490 

Description   490 

The  Male 491 

Dispersion 491 

Seasonal  History 491 

The  Six-spotted  Mite  (Teiranychus  sexmaculatus  Riley) 492 

Distribution  in  California 492 

Nature  of  Injury 493 

Life  History  and  Habits 493 

The   Egg  493 

The   Young  Mite 493 

The  Adult 493 

Seasonal  History 494 

The  Silver  or  Rust  Mite  (Eriophyes  oleivorus  Ash.) 494 

Nature  of  Injury 495 

Distribution    496 

Description,  Life  History.  Habits 496 

The  Egg 496 

The  Young  Mite 497 

The  Adult —  497 

Tenaipalpus  californicus  Banks 497 

Tetranychoides  californicus  Banks 498 

Caligonus  terminalis  Banks 499 

Tetranychus  bimaculatus  Harvey 500 

Bryobia  pratensis  Garmen 501 

Tyroglyphus  americanus  Banks 502 

Gamasid  sp.   502 

Gamasid  sp.   503 

Tarsonemus  approximates  Banks  Mss 503 

Tarsonemus  assimids  Banks  Mss 503 

Eremceus  modestas  Banks 504 

Key  to  the  Species 505 


tvt    .         ,    T,          .  Page. 

Natural  Enemies 595 

Conventzia  hageni 500 

The   Egg   506 

The  Larva : 507 

Feeding   of   Larva 508 

Pupation  and  Cocoon 508 

The  Pupa  509 

The  Adult 509 

Oligota  oviformis  Csy 509 

Description,  Life  History,  Habits 509 

The   Egg   509 

The  Larva 510 

Manner  of  and  Capacity  for  Feeding 510 

The  Adult 511 

Stcthorus   picipes   Csy 511 

Description,  Life  History,  Habits 511 

The    Egg    511 

The   Larva    512 

The  Pupa  512 

The  Adult 513 

Scolothrips  sexmaculatus  Pergande 513 

Arthrocnodax  occidentalis   Mss 514 

Parasite  of  Arthrocnodax 515 

Thriphleps  insidiosus  Say 51G 

The   Brown    Lacewing 516 

The   Green   Lacewing 518 

Other  Enemies 519 

The  Control  of  Spiders  and  Mites  on  Citrus  Trees 519 

Fumigation   Not  Effective . 519 

Lime  Sulphur  Spray 521 

Dilutions   521 

Cost 522 

What  the  Spray  Does 522 

Dry    Sulphur    523 

How  the  Sulphur  Acts 523 

How  Applied 524 

When  the  Application  Should  be  Made 524 

Materials     527 

Dry  Sulphuring  the  Fruit  Pickers 527 

The  Dry  versus  the  Liquid  Spray 527 

Distillate  or  Kerosene  Emulsion _ 529 

Other  Sprays   530 

Summary 530 


RED  SPIDERS  AND  MITES  OE  CITRUS  TREES. 

By  H.  J.  Quayle. 


INTRODUCTION. 

Next  to  the  scale  insects,  red  spiders  and  mites  are  the  most  important 
pests  of  citrus  trees  in  California.  On  account  of  their  small  size,  and 
because  the  foliage  and  fruit  of  the  tree  are  not  conspicuously  marred 
cither  by  their  presence  or  by  the  covering  of  sooty  mold  fungus,  as  is 
the  case  with  some  of  the  scale  insects,  the  actual  injury  done  by  red 
spiders  and  mites  is  not  always  appreciated.  Their  distribution  is  very 
general  over  the  citrus  sections,  and  they  may  be  found  in  some  numbers 
at  most  any  season  of  the  year.  So  long  as  they  do  not  become  numer- 
ous the  injury  they  do  is. not  important  and  in  such  cases  it  is  not  good 
economy  to  apply  treatment.  Because  of  their  more  or  less  continual 
presence  in  scattering  numbers  some  growers  take  red  spiders  as  a  mat- 
ter of  course,  and  fail  to  recognize  their  importance  when  they  become 
abundant  and  do  damage,  or  come  to  a  realization  of  their  injurious 
nature  after  most  of  the  damage  has  been  done  and  the  spiders  them- 
selves begin  to  disappear,  as  they  often  do.  While,  therefore,  the 
presence  of  spiders  in  scattering  numbers  should  be  the  cause  of  no  par- 
ticular concern,  the  presence  of  excessive  numbers  of  spiders  should  be 
the  cause  of  enough  concern  for  the  grower  to  start  immediately  to  apply 
control  measures.  Dropping  of  the  leaves  and  fruit  is  the  ultimate 
result  of  red  spider  injury.  But  the  cause  should  be  checked  long 
before  this  extreme  effect  is  evident. 

Nature  of  Injury.  The  first  indication  of  red  spider  work  is  to  be 
seen  in  the  pale  spots,  scattered  about  over  the  leaf  surface,  which  rep- 
resent their  feeding  places.  In  the  case  of  the  commonest  species  these 
areas  are  very  small  and  represent  often,  probably,  but  a  single  insertion 
of  their  mouth  parts.  In  the  next  most  important  species  on  citrus  trees, 
the  feeding  is  restricted  very  largely  to  definite  areas,  and  these  become 
yellowish  in  color  and  conspicuous  even  from  a  distance.  A^JJoe 
feeding  areas  become^  numerous- most o£  the-functional  green  matter  in 
the  leaf  is  absorbed,  and  such  a  leaf  assumes  a  grayish  or  yellowish  color 
and  is  of  little  use  to  the  tree.  Leaves  thus  affected  fall  prematurely, 
and  sometimes  there  is  a  heavy  denudation  as  a  result  of  red  spider 
injury. 

As  a  rule  red  spiders  are  most  numerous  in  the  spring,  April,  May, 
and  June.  Anything  that  tends  to  diminish  the  vigor  of  the  tree  at 
this  time,  as  an  impairment  or  dropping  of  the  leaves,  must  have  its 
effect  on  the  setting  or  maintenance  of  the  crop.  Aside  from  this,  how- 
ever, the  spiders  attack  the  fruit  directly.     The  pale  silvery  color  of 


484 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


green  fruit  is  characteristic  of  red  spider  or  mite  injury.  Such  fruit 
either  falls  from  the  tree  or  never  attains  its  usual  color.  While  spring 
is  the  most  favorable  season  for  spiders,  they  often  become  abundant 
also  in  the  fall,  and  less  often  at  other  seasons.  Some  of  the  worst 
effects  of  red  spider  injury  noted  by  the  writer  occurred  in  the  fall  and 
early  winter  of  1911.  At  this  time  as  the  fruit  is  maturing  the  spiders 
give  it  a  pale  lusterless  yellow  color,  instead  of  the  normal  bright  orange. 
This  change  in  the  ripening  fruit,  in  the  case  of  Valencias,  may  be  due 
also  to  the  spring  crop  of  spiders. 


Fig.  1. — Top  of  a  citrus  tree  partially  defoliated  by  work  of  Red  Spiders. 

Another  phase  of  injury  which  has  often  been  brought  to  our  atten- 
tion is  the  possibility  of  spiders  and  mites  being  responsible  for  the  dis- 
tribution of  fungus  spores  and  thus  indirectly  disfiguring  the  fruit  or 
starting  infection  on  the  more  tender  twigs.  While  such  effects  are  still 
obscure,  there  is  every  likelihood  that  red  spiders,  by  their  moving 
about  from  one  place  to  another  and  making  abrasions  in  the  epidermis, 
might  be  the  means  of  spreading  fungous  or  bacterial  troubles.  A  red- 
dish stain  sometimes  develops  on  the  fruit  even  long  after  the  attacks  of 
the  spiders  and  this  is  often  attributed  to  their  work.     Still  another 


Bulletin  234] 


RED    SPIDERS    AND    MITES    OF    CITRUS    TREES. 


485 


effect  of  such  pests,  which  is  indicated  very  strongly  by  our  general 
observations,  is  that  they  appear  sometimes  to  be  the  primary  cause  of 
the  dying  back  of  the  tips  of  the  twigs.  Where  twigs  are  defoliated  by 
their  work,  they  may  be  killed  or  greatly  weakened  and  such  twigs  are 
then  likely  to  be  attacked  by  other  troubles  such  as  the  ' '  wither-tip " 
fungus  and  die-back.  It  occasionally  happens  that  red  spiders  give 
trouble  in  packing-houses  by  continuing  to  breed  on  the  fruit,  partic- 
ularly the  lemon,  during  curing  or  storage.  It  is  possible,  also,  that 
mites  may  aid  in  the  spread  of  decay  infections  while  the  fruit  is  in 
transit.  After  lemons  had  been  kept  in  a  tightly  covered  glass  dish  in 
the  laboratory  for  six  or  seven  months  we  have  taken  numerous  mites 
representing  three  different  species. 


Fig.  2. — Orange  twigs  defoliated  by  Red  Spiders. 


Species  Concerned. — Red  spiders  and  mites  belong  to  the  order 
Acarina,  of  the  class  Arachnida,  and  are,  therefore,  not  insects  which 
are  included  in  the  class  Insecta.  Structurally,  spiders  and  mites  differ 
from  insects  in  having,  usually,  four  pairs  of  legs  instead  of  but  three  as 
insects  do,  and,  further,  in  that  the  body  is  not  divided  into  three  dis- 
tinct regions,  head,  thorax  and  abdomen,  as  is  characteristic  of  adult 
insects.     Practically,  in  so  far  as  it  relates  to  their  control  on  citrus 


486 


UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 


trees,  they  differ  from  most  insects  because  they  are  not  killed  by  the 
ordinary  fumigation  dosages. 

There  have  been  recognized  three  more  or  less  well  known  species  of 


Fig.  3. — Orange  leaves  showing  work  of  Six-spotted  Mite. 

spiders  and  mites  that  attack  citrus  trees  in  California.  These  are  the 
citrus  red  spider  (Tetranychus  mytilaspidis  Riley),  the  six-spotted  mite 
(Tetranychus  sexmaculatus  Riley)   and  the  citrus  rust  mite  or  silver 


Bulletin  234]         EED    SpIDERS    AND    MITES    OF    CITRUS   TREES.  487 

mite  (Eriophyes  oleivorus  Ash.).  The  present  studies  have  brought  out 
several  other  species  that  are  found  on  citrus  trees,  but  none  of  these 
rank  in  importance  with  the  three  mentioned.  In  the  following  pages 
the  species  are  discussed  separately  in  the  order  of  their  importance, 
and  following  this  the  different  species  of  natural  enemies  receive  con- 
sideration. Practical  growers  who  are  interested  chiefly  in  how  to  con- 
trol spiders  and  mites  will  find  a  discussion  of  such  measures  on  page 
519  and  a  summary  account  of  this  bulletin  on  page  530. 

Mr.  J.  D.  Neiils,  who  has  assisted  the  writer  during  the  present  year 
has  made  many  of  the  observations  herein  recorded. 

THE  CITRUS  RED  SPIDER. 
(Tetranychus  mytilaspidis  Riley.) 

Early  Account. — This  species  was  first  described  from  specimens 
taken  from  the  orange  in  Florida  in  1885.*  It  was  introduced  into  Cali- 
fornia from  Florida  on  nursery  stock  in  about  1890.  It  doesn't  appear 
to  be  as  injurious  in  Florida  as  sexmaculatus,  while  in  California  it  is 
much  more  injurious  than  the  latter  species.  Mytilaspidis  has  been  a 
pest  in  the  State  since  about  1895.  Early  in  1900  a  demand  was  made 
from  the  citrus  growers  for  a  study  of  the  spider  because  of  its  injurious 
nature,  and  also  because  of  its  supposed  relation  to  the  spotting  of  the 
fruit  due  to  the  old  distillate  spray,  and  a  bulletin,  now  out  of  print, 
was  issued  by  Professor  Woodworth  in  1902. 

Nature  of  Injury. — This  species  causes  the  more  characteristic  mite 
injury  as  represented  at  first  by  pale  colored  specks  over  the  surface  of 
the  leaf  and  fruit,  these  gradually  increasing  in  numbers  until  they 
become  numerous  enough  to  produce  a  general  pale  gray  or  silvery 
effect  over  the  whole  of  the  leaf  and  fruit.  The  leaves  are  the  first  to 
show  this  effect  and  later  the  fruit.  The  tender  twigs  are  also  attacked 
and  when  the  spiders  are  abundant  numerous  eggs  and  cast  skins  will 
be  found  on  them.  This  is  the  species  that  has  given  the  most  trouble 
in  the  packing-house  because  it  so  readily  attacks  the  fruit.  It  is  dis- 
tinctly the  most  injurious  of  all  the  species  found  on  citrus  trees. 

Distribution. — The  citrus  red  spider  is  the  most  widely  distributed 
of  all  the  species  and  is  the  one  that  most  control  work  is  directed 
against.  It  occurs  very  commonly  in  San  Diego  County,  as  well  as 
elsewhere,  but  there  the  six-spotted  mite  is  sometimes  more  important. 
Mytilaspidis  has  been  presumed  to  be  limited  to  the  citrus  fruits,  and, 
consequently  occuring  in  California,  Florida  and  elsewhere  where  citrus 
fruits  are  grown.  Mr.  H.  E.  Ewing  states,  however,  that  he  finds  the 
species  a  pest  on  plum,  prune  and  other  deciduous  trees  in  Oregon,  and 
we  have  taken  it  on  apple  and  some  of  the  other  deciduous  trees  growing 
among  the  citrus  trees  in  southern  California. 

♦Hubbard,  H.  G.     Insects  Affecting  the  Orange.     Div.  Ent,  U.  S.  D.  A.,  1885. 


488  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

It  has  not  been  reported  as  injurious  thus  far  from  the  citrus  section 
of  the  San  Joaquin  or  Sacramento  valleys,  but  is  generally  distributed 
in  the  citrus  sections  south  of  the  Tehachapi.  In  the  citrus  section  this 
species  is  restricted  almost  entirely  as  a  pest  to  citrus  trees.  Reports  of 
the  spiders  overrunning  everything  as  ornamentals,  vegetables  and  cover 
crops  have  been  frequent,  but  in  every  case  they  have  not  proved  to  be 
T.  mytilaspidis.  On  ornamentals  particularly  violets,  and  such  vege- 
tables as  beans,  the  species  is  generally  T.  bimacidatus.  On  almond  and 
apricot  trees,  and  on  such  cover  crops  as  vetch,  the  species  is  usually 
Bryobia  pratensis.  Almond  trees  surrounded  on  all  sides  and  imme- 
diately adjoining  citrus  trees  are  usually  infested  with  the  latter  species. 

Mytilaspidis  is  a  species  well  adapted  to  the  warmer  and  dryer  sec- 
tions, althought  it  is  not  limited  to  such  conditions.  The  fact  that  it  is 
more  injurious  here  than  in  Florida  and  its  distribution  in  this  State 
is  general  in  the  interior  sections  appears  to  indicate  this ;  while  sexma- 
cidatus  is  the  more  injurious  of  the  two  in  Florida,  and  its  distribution 
here  is  limited  to  the  Coast  counties  making  it  a  species  better  adapted 
to  more  humid  conditions. 

LIFE  HISTORY  AND  HABITS. 

THE   EGG. 

Appearance. — The  egg  of  mytilaspidis,  see  outside  cover,  differs  from 
that  of  all  other  species  found  on  citrus  trees  by  the  presence  of  guy 
threads  radiating  from  the  top  of  a  vertical  stalk.  It  sometimes 
happens  that  the  eggs  of  some  of  the  other  species  will  have  a  more  or 
less  indefinite  stalk,  but  they  never  have  the  supporting  guy  threads,  or 
even  a  regular  or  definite  stalk.  The  egg  itself  is  spherical  in  shape  but 
slightly  flattened  at  the  poles.  When  first  laid  it  is  uniformly  bright 
red  in  color,  but  later  this  color  pigment  gathers  in  particular  areas, 
usually  at  one  side  and  finally  the  eyes  and  outline  of  the  developing 
spider  can  be  made  out.  The  stalk  arises  vertically  and  measures  about 
twice  the  diameter  of  the  egg.  From  the  top  of  the  stalk  there  radiate, 
in  a  somewhat  regular  manner,  from  twelve  to  fourteen  guy  threads 
which  extend  down  to  the  leaf,  forming  a  tent-like  arrangement  over  the 
egg.  As  soon  as  the  egg  is  deposited  the  abdomen  is  raised  to  form  the 
stalk,  and  afterward  move  from  the  top  of  the  stalk  to  the  leaf  several 
times,  thus  forming  the  supporting  guys.  The  purpose  of  these  radiat- 
ing threads  may  be  to  hold  the  egg  in  place,  though  this  could  be 
accomplished  by  the  secretion  of  an  adhesive  substance  which  is  the 
usual  way.  They  may  be  for  protective  purposes,  since  the  egg  is 
enclosed  in  a  canopy  of  these  threads  which  may  deter  some  of  the 
natural  enemies  from  reaching  them.  It  must  be  said,  however,  that 
the  enemies  discussed  farther  along  were  not  observed  to  be  limited  by 


Bulletin  234]         RED    SPIDEKs    AND    MITES    OF    CITRUS    TREES.  489 

this  frail  stockade.  In  the  case  of  sexmaculatus  the  eggs  are  protected 
to  a  considerable  extent  by  being  deposited  beneath,  or  entangled  in,  a 
more  dense  network  of  web. 

Number.— The  number  of  eggs  produced  by  this  species  will  average 
about  thirty,  or  at  least  this  represents  what  we  have  been  able  to  obtain 
under  conditions  as  nearly  natural  as  possible.  The  average  number 
deposited  per  day  for  the  producing  period  will  be  between  two  and 
three.  Some  days  as  many  as  six  or  seven  may  be  deposited  but  other 
days  but  one  or  two  and  occasionally  none.  As  an  illustration,  daily 
records  made  on  the  deposition  of  285  eggs  show  that  they  were  depos- 
ited in  113  days  by  13  spiders.  This  is  an  average  of  two  or  three  a 
day  and  an  average  of  22  eggs  for  each  spider.  Some  of  these,  however, 
were  not  counted  for  the  full  ovipositing  period. 

Proportion  Hatching. — Ordinarily  a  large  proportion  of  the  eggs 
hatch  if  they  are  not  attacked  by  predaceous  enemies.  Thrips, 
Coniopteryx,  Staphylinid  beetle,  syrphus  fly  and  lacewing  larvse  all  may 
attack  red  spider  eggs.  Sometimes,  however,  the  reason  for  not  hatching 
is  unknown  and  occasionally  the  percentage  thus  failing  to  hatch  will 
reach  as  high  as  50  per  cent.  ^ 

Period  of  Incubation. — The  time  required  for  the  eggs  to  hatch  varies 
from  eight  to  ten  days  in  summer  to  three  weeks  or  even  longer  in  win- 
ter. During  the  season  when  they  are  most  abundant  about  ten  days 
will  be  the  average  hatching  period. 

THE  YOUNG. 

Appearance  and  Emergence. — The  young  spider  is  very  much  like 
the  adult  excepting  that  it  is  smaller  in  size  and  has  but  three  pairs  of 
legs.  The  fourth  pair  is  acquired  upon  the  first  molt.  The  egg  splits 
in  an  even  line  around  the  equatorial  zone  and  through  the  efforts  of  the 
spider  the  parts  are  separated  on  one  side  as  though  hinged.  The  fore 
legs  and  front  part  of  the  body  are  first  freed,  and  often  when  in  this 
stage  of  emergence  they  apparently  insert  their  mouth  parts  and  begin 
to  feed.  When  they  finally  crawl  out,  the  two  halves  of  the  eggshell 
which  have  been  held  apart  by  the  emerging  spider  spring  back  into 
place  again.  It  is  now  perfectly  transparent,  but  otherwise  appears  as 
a  normal  egg.  Sometimes  the  parts  of  the  egg  covering  may  remain 
separated,  and  in  such  cases,  that  hatching  has  occurred  is  very  evident. 
Where  the  egg  is  simply  transparent  it  may  be  due  to  the  attacks  of  one 
of  several  enemies,  and  to  determine  whether  the  egg  has  hatched  or  not 
it  is  necessary  to  examine  closely  enough  to  make  out  the  crack  in  the 
shell. 

Feeding  begins  just  as  soon  as  the  young  emerge.  On  the  second  or 
third  day  the  first  molt  occurs.  After  two  or  three  days  more  the  second 
molt  takes  place  and  a  similar  period  elapses  for  the  third  and  last  molt. 
In  a  majority  of  cases  three  days  represent  the  period  between  hatching 
and  the  first  molt,  while  between  the  other  molts  two  days  is  very  fre- 
quently the  period.     This  is  based  upon  records  of  upwards  of  a  hun- 


490  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

dred  spiders.  It  not  infrequently  happens  that  the  male  completes  its 
development  in  one  day  less  than  the  female,  and  males  have  often  been 
seen  to  assist  the  females  in  freeing  themselves  from  their  last  cast  skin. 
Process  of  Molting.— Preceding  the  actual  discarding  of  the  old  skin 
the  spider  is  quiet  for  some  time  and  becomes  much  paler  in  color,  par- 
ticularly the  appendages.  With  the  light  colored  species  the  old  skin 
can  be  distinguished  by  its  transparency  just  preceding  the  molt.  The 
skin  is  split  transversely  around  the  middle  of  the  body  between  the 
second  and  third  pairs  of  legs.  By  raising  the  center  of  the  body 
upward  the  parts  of  the  old  skin  are  separated  on  the  dorsal  surface. 
The  front  part  of  the  body  is  then  pulled  out  of  its  old  covering,  and  the 
front  legs  being  free,  it  pulls  itself  or  simply  walks  out  of  the  posterior 
pocket.  Sometimes  the  latter  adheres  to  the  spider  until  after  it  has 
traveled  some  little  distance  so  the  two  halves  of  the  cast  skin  are  separ- 
ated. In  other  cases  the  break  does  not  occur  on  the  ventral  surface 
and  the  parts  are  kept  together. 


Fig.    4.— The  Citrus  Red  Spider. 
Tetranychus  mptilaspidis  Riley. 

THE  ADULT. 

Description. — The  citrus  red  spider,  T.  pvytilaspidis,  is  not  difficult  to 
distinguish  from  all  the  others  found  on  crtrT3§~rrees.  It  is  distinctly 
red  in  color,  though  different  shades  of  red  may  be  represented  in  dif- 
ferent individuals.  Most  commonly  it  is  of  a  dark  velvety  color  and  not 
smooth  and  shiny  as  are  some  of  the  other  associated  species.  In  size 
it  is  larger  than  most  others  found  with  it,  the  body  being  robust  and 
rounded  above.  One  of  the  definite  characters  that  serves  to  distinguish 
this  species  from  other  members  of  the  same  genus  is  that  the  bristles 
covering  the  body  arise  from  prominent  tubercles.  The  bristles  are 
large  and  white  in  color.  Only  one  other  species  of  the  genus  Tetrany- 
chus has  the  tubercles  and  this  is  not  found,  thus  far,  on  citrus  trees. 
Since  eggs  are  usually  found  with  the  spiders,  an  examination  of  these 
eggs  for  the  stalk  and  radiating  guy  threads  will  serve  to  distinguish  the 


Bulletin  234]         RED    SPidEKS   AND    MITES    OF    CITRUS   TREES.  491 

species.     For  the  more  technical  characters  that  separate  the  species  see 
table  on  page  505. 

The  Male. — The  male  of  this  species,  as  is  true  with  most  others,  is  con- 
siderably smaller  than  the  female.  Instead  of  the  body  being  robust 
and  oval,  as  is  the  female,  it  becomes  more  narrowed  and  pointed  poster- 
iorly. The  body  of  the  male  is  capable  of  considerable  telescopic  action 
which  is  evident  in  pairing  when  it  is  greatly  extended  and  curved 
upward,  the  female  being  above.  Eggs  will  be  deposited  in  the  absence 
of  fertilization  and  these  normally  hatch  into  individuals  of  the  male 
sex  only.  Out  of  81  eggs  laid  by  unfertilized  females  65  hatched  and  all 
were  males.  The  production  of  males  only  from  unfertilized  eggs 
appears  to  be  the  case  also  with  T.  bimaculatus.  Out  of  34  unfertilized 
eggs  laid  by  this  species  27  hatched  and  all  were  males. 

Dispersion.— Red  spiders  of  this  species  are  very  active  and  may 
travel  about  very  generally  over  the  tree,  but  usually  they  remain 
throughout  their  life  on  the  same  or  adjoining  twigs.  The  fact  that 
they  are  found  on  the  ground  is  not  an  indication  that  they  live  there  or 
may  develop  there.  Those  that  occur  on  the  ground  have  fallen  there, 
either  by  themselves,  or  upon  a  leaf,  or  have  crawled  down  the  tree 
trunk.  They  can  also  make  considerable  headway  on  the  ground  and 
thus  reach  other  near-by  trees  by  their  own  powers/  of  locomotion. 
Several  experiments  to  determine  the  rate  of  travel  over  orchard  soil 
indicate  that  they  may  travel  on  an  average  at  the  rate  of  from  4  inches 
to  10  inches  in  an  hour.  From  two  to  four  days  is  the  maximum  period 
they  will  live  without  food.  They  are  also  very  quickly  killed  on  the 
ground  with  a  temperature  of  110  degrees  or  higher.  A  grove  that 
received  very  efficient  treatment  in  the  fall  of  1911  was  entirely  free 
from  spiders,  even  well  into  the  season  of  1912,  with  the  exception  of  the 
first  few  outside  rows.  The  adjoining  groves  had  many  spiders,  and  it 
seemed  very  evident  that  those  on  the  margins  of  the  treated  grove 
became  infested  from  these,  and  through  the  movement  of  the  spiders 
themselves.  In  addition,  birds  and  insects,  as  well  as  man  in  his  general 
cultural  operations,  may  be  responsible  for  more  or  less  dispersion  of  the 
spiders. 

Seasonal  History. — The  citrus  red  spider  appears  in  greatest  num- 
bers during  May  and  June.  With  the  higher  temperatures  of  midsum- 
mer their  numbers  may  decrease  considerably  or  almost  entirely  disap- 
pear. Commonly  they  do  not  again  appear  in  large  numbers  until  the 
following  spring.  But  exceptions  occur  to  this,  and  not  infrequently 
they  become  abundant  in  the  late  fall  or  early  winter. 

It  is  not  possible  to  state  definitely  the  number  of  generations  that 
occur  in  a  season.  Spiders  will  be  found  in  all  stages  at  nearly  all  sea- 
sons of  the  year.  During  the  warmer  season,  from  May  to  October,  the 
period  from  hatching  to  maturity  will  be  just  three  weeks.  During  the 
colder,  wet  season  it  will  be  extended  to  five  weeks,  most  of  this  addi- 
tional time  being  required  for  the  eggs  to  hatch.     On  this  basis  there 


492 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


may  be  from  12  to  15  generations  during  the  year.  The  entire  life  cycle 
from  hatching  to  the  death  of  the  adult  occupies  from  thirty-five  to 
forty  days,  divided  as  follows :  egg  ten  days,  first  stage  three  days,  sec- 
ond stage  three  days,  third  stage  three  days ;  adult  eighteen  days.  Mat- 
ing occurs  immediately  after  the  last  molt  and  egg  laying  begins  from 
two  to  three  days  later. 

The  natural  enemies  of  this  species  will  be  found  discussed  on  page 
505  and  control  measures  on  page  519. 


THE  SIX-SPOTTED  MITE. 
(Tetranychus  sexmaculatus  Riley.) 

This  mite  first  came  into  prominence  as  a  pest  on  orange  trees  in 
Florida  in  1886.  Brief  mention  is  made  of  it  by  Hubbard  in  1885  but 
no  adequate  description  appeared  until  it  was  described  by  Riley  in 
1890.*  It  was  first  recorded  on  the  wild  orange  in  Florida  and  later 
became  a  pest  on  other  species  of  citrus.  In  the  report  of  the  Secretary 
of  Agriculture  for  1889,  Riley  has  also  given  a  discussion  of  its  life  his- 
tory and  economic  importance.  In  this  account  one  of  the  common 
names  then  known  to  be  applied  was  "California  spider,"  and  from 
this  it  would  appear  that  it  was  known  in  this  State  at  least  as  early  as 
1889.  That  it  wras  introduced  into  this  State  on  nursery  stock  from 
Florida  in  the  late  eighties  appears  to  be  fairly  well  established. 


Fig.    5. — The   Six- spotted   Mite,    Tetranychus 
sexmaculatus  Riley.     Palpus  on  left. 

Distribution  in  California. — The  six-spotted  mite  is  most  important  as 
a  pest  in  San  Diego  County.  It  is  widely  distributed  throughout  that 
section.  It  also  occurs  in  Los  Angeles,  Orange,  and  Santa  Barbara 
counties,  but  very  scattering,  only  a  few  trees  here  and  there  or  an  occa- 
sional grove  will  be  found  infested.  We  have  not  taken  it  in  Riverside 
and  San  Bernardino  counties  and  the  horticultural  commissioners  of 
those  counties,  Mr.  Cundiff  and  Mr.  Pease,  state  that  it  does  not  occur 

*C.  V.  Riley.     Insect  Life,  Vol.  II,  p.  225. 


Bulletin  234]         RED    SPIDERS    AND    MITES    OF    CITRUS   TREES.  493 

there  to  their  knowledge.  Neither  has  it  been  taken,  thns  far,  from 
Ventura  County.  From  its  more  general  distribution  along  the  coast  it 
appears  to  be  a  mite  better  adapted  to  regions  of  more  moisture. 

Nature  of  Injury. — The  work  of  the  six-spotted  mite  is  very  charac- 
teristic and  is  easily  distinguished  from  that  of  all  the  other  species. 
This  mite  is  very  definitely  confined  to  particular  areas.  These  are  on 
the  under  side  of  the  leaf  and  usually  along  the  midrib  or  larger  veins 
but  sometimes  close  to  the  margin.  There  is  a  distinct  depression 
formed  where  the  colony  has  its  headquarters.  This  depression  is  of  a 
pale  yellowish  color  and  is  covered  with  a  web  which  protects  the  spiders 
beneath,  and  which  also  serves  as  a  support  for  the  eggs  which  will  be 
seen  scattered  about  entangled  in  the  silk.  Beneath  this  web  the  leaf 
surface  is  a  yellowish  color,  due  to  their  feeding,  and  there  are  present 
also  the  molted  skins  and  small  black  particles  of  excrement.  On  the 
upper  surface  of  the  leaf  this  same  area  is  represented  by  a  raised  por- 
tion or  swelling  which  is  distinctly  yellow,  or  yellowish  white  in  color, 
and  has  a  smooth  shiny  surface.  In  cases  of  severe  injury  by  these  mites 
these  areas  may  make  up  the  greater  portion  of  the  leaf,  and  such  leaves, 
particularly  if  they  are  growing  leaves,  become  very  badly  distorted 
and  misshapen. 

LIFE  HISTORY  AND  HABITS. 

The  Egg. — The  egg  of  this  species  is  white  or  yellowish  white  in  color 
and  perfectly  round.  The  eggs  will  be  found  in  the  areas  where  the 
mites  feed  and  are  usually  entangled  in  the  web  which  serves  as  a  pro- 
tection, or  they  will  be  found  on  the  leaf  surface  beneath  this  web. 
From  twenty-five  to  forty  eggs  will  be  deposited  during  a  period  of  ten 
to  twenty  days.  They  require  five  to  eight  days  for  hatching  in  June. 
This  will  be  extended  to  three  weeks  during  the  winter  months. 

The  Young  Mite. — A  young  mite  that  hatched  from  the  egg  on  July 
10th  molted  on  the  12th,  two  days  later.  The  fourth  pair  of  legs,  as  in 
the  other  species,  appears  after  this  molt.  The  second  molt  occurred  on 
the  14th  and  the  third  and  last  molt  on  the  16th.  This  mite  was  a  male. 
Another  hatched  on  the  same  day,  molted  on  the  12th,  14th  and  17th. 
This  one  was  a  female  and  required  one  day  longer.  It  often  happens 
that  the  male  will  complete  its  development  in  one  day  less  than  the 
female.  The  two  specific  cases  given  represent  the  time  required  for  the 
development  of  the  mite  during  June  and  July,  as  determined  from  a 
number  of  rearing  records.  It  thus  requires  from  six  to  nine  days  for 
the  development  of  this  species,  and  allowing  two  or  three  days  more 
before  egg-laying  begins  the  total  period  from  the  egg  to  maturity  will 
be  from  eight  to  twelve  days.  The  manner  of  molting  and  other  details 
in  development  are  essentially  the  same  as  in  the  previous  species,  which 
has  already  been  discussed. 

The  Adult.— The  adult  of  this  species  is  generally  smaller  than 
mytilasphidis,  and  it  is  never  red  in  color.  The  color,  however,  varies 
greatly  and  in  some  a  considerable"  amount  of  the  dark  pigment  will  be 


494  UNIVEKSITY    OF   CALIFORNIA EXPERIMENT    STATION. 

seen  and  some  indication  of  this  pigment  coalesced  into  six  areas  or 
spots,  hence  the  name  sexmaculatus  or  six-spotted  mite;  but  in  others 
no  trace  of  pigment  is  present  and  the  mite  will  appear  of  a  uniform 
light  pink  or  pale  greenish  yellow  color.  It  is  clothed  with  many  hairs 
but  there  are  not  so  long  as  in  mytilaspidis  nor  do  they  arise  from 
tubercles.  This  six-spotted  mite  is  thus  easily  distinguished  from  the 
citrus  red  spider,  but  it  is  not  so  easily  distinguished  from  Tetranychus 
bimaculatus,  or  the  common  red  spider.  Indeed,  structurally  they 
are  very  similar,  the  difference  is  supposed  to  be  in  the  number  of 
fingers  on  the  thumb  of  the  palpi  and  this  seems  to  be  variable.  But  the 
bimaculatus  that  occurs  on  violets,  beans,  and  many  other  plants  in  the 
citrus  belt  is  not  only  different  in  habits,  but  the  mite  itself  is  very  dif- 
erent  as  regards  coloring,  though  occasionally  the  difference  is  not  so 
distinctly  marked.  This  question  of  identity  is  discussed  further  under 
bimaculatus  on  page  500. 

Eggs  are  deposited  at  the  rate  of  from  two  to  five  a  day  for  a  period 
of  ten  or  fifteen  days.  While  the  adult,  as  well  as  the  young,  may  fre- 
quently be  found  away  from  their  web-protected  home,  feeding  must  be 
largely  restricted  to  the  areas  protected  by  the  web  since  no  other  parts 
of  the  leaf  show  such  serious  injury.  In  a  bad  infestation  of  course 
these  areas  cover  nearly  the  entire  leaf. 

Seasonal  History. — This  species  becomes  most  abundant  usually  in  the 
spring  or  early  summer.  Very  severe  defoliation  from  this  species  has 
been  seen  in  May  and  June,  but  not  infrequently  sulphur  is  applied  in 
San  Diego  to  control  them  in  August  and  September.  Sometimes  they 
also  become  abundant  during  a  warm,  dry  period  in  midwinter.  Since 
the  eggs  hatch  in  five  to  eight  days,  eight  to  twelve  days  are  required  for 
the  development  of  the  young,  and  the  adult  lives  ten  to  fifteen  days,  the 
complete  life  cycle  requires  from  three  to  four  weeks.  Seasons  when 
they  are  not  noticeable  or  abundant  doesn't  mean  that  they  have  disap- 
peared entirely,  but  that  breeding  is  occurring  so  slowly  as  to  make 
their  effect  on  the  tree  inconspicuous.  One  generation  follows  another 
more  or  less  irregularly  throughout  the  season,  and  there  are  a  total  of 
from  twelve  to  fifteen.  The  control  of  this  species  is  given  beginning 
on  page  519. 

THE  SILVER  OR  RUST  MITE. 
(Eriophyes  oleivorus  Ash.) 

The  silver  or  russet  mite  was  introduced  into  this  State  from  Florida 
in  1889.  It  is  called  the  rust  mite  in  Florida  because  of  the  brown  or 
russet  effect  it  produces  on  the  oranges,  the  principal  variety  of  fruit 
grown  there.  In  this  State  it  is  known  as  the  silver  mite  because  of  the 
white  or  silvery  effect  it  produces  on  the  lemon,  the  principal  variety  of 
citrus  grown  in  the  section  of  the  State  where  it  occurs.  This  mite  was 
originally  described  from  Florida,  and  is  known  to  attack  only  the  dif- 
ferent varieties  of  citrus.  It  is  probably  a  native  of  Florida  where  the 
wild  orange  served  as  its  original  food  plant. 


Bulletin  234] 


RED    SPIDEES    AND    .MITES    OF    CITRUS   TREES. 


495 


This  species  belongs  to  a  very  different  group  of  mites  than  the  ones 
thus  far  discussed.  It  belongs  to  the  family  Eriophyidce  which  include 
small  four-legged  mites  of  a  vermiform  or  worm-like  shape,  and  so  small 
as  to  be  scarcely  visible  to  the  naked  eye.  In  this  family  are  included 
the  leaf -blister  mite  of  the  apple  and  pear;  another  causes  the  erinose  of 
the  grape,  and  another  a  similar  affection,  characterized  by  fuzzy  brown 
spots,  on  the  leaves  of  the  English  walnut. 


Fig.  6. — Silver  Mite. 

Nature  of  Injury. — The  silver  mite  has  mouth  parts  similar  to  the  red 
spider,  and  the  manner  of  injury  is  much  the  same.  But  the  ultimate 
effect  of  silver  mite  injury  is  easily  distinguished  from  red  spider  or 
other  mite  injury.  This  may  be  partly  because  it  becomes  more  numer- 
ous and  the  injury  is  more  pronounced,  for  a  mild  case  of  silver  mite 


.#3§V 

Hi 

$^§fejsgk 

^ ■..""■":    '■' 

^  4 

'               *  . 

~ 

Fig.  7. — Lemon  on  right  showing  work  of  Silver  Mite. 

injury  may  be  difficult  to  distinguish  from  the  citrus  red  spider  injury. 
A  lemon  badly  infested  with  silver  mite  becomes  distinctly  white  or 
silvery  in  color  and  much  more  pronounced  than  in  the  severest  attack 
of  mytilaspidis.  Silver  mite  injury  is  much  more  restricted  to  the  fruit, 
while  the  others  really  produce  injury  to  the  leaves  first.  It  is  also  often 
confined  to  a  more  or  less  definite  area  on  the  fruit,  as  the  upper  side, 
while  red  spider  injury  is  more  uniform.     The  rind  of  lemons  that  have 

2—234 


496  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

been  injured  by  silver  mite  becomes  very  hard  and  is  covered  with  a  net- 
work of  cracks. 

The  attacks  of  this  mite  affect  the  lemon  somewhat  differently  from 
the  orange.  The  ripening  orange  becomes  very  distinctly  browned  or 
russeted,  while  on  the  lemon  the  characteristic  injury  is  the  white  or 
silvery  appearance.  But  this  difference  is  not  so  great  as  it  apparently 
seems.  On  both  the  orange  and  lemon,  while  they  are  small  or  green, 
the  effect  is  similar,  though  the  silvered  appearance  is  more  marked  in 
the  case  of  the  lemon.  Since  the  lemon  is  picked  when  it  attains  a  cer- 
tain size,  and  is,  hence,  usually  green,  the  brown  color  has  not  yet  devel- 
oped, while  the  orange  is  allowed  to  ripen  on  the  tree  and  the  brown  or 
russet  effect  becomes  very  evident.  In  case  of  the  tree-ripe  lemons  the 
browned  effect  is  apparent,  but  never  so  marked  as  with  the  orange. 
This  silvered,  and  later,  russet,  effect  is  due  to  the  mites  taking  up  the 
oils  and  green  matter  from  near  the  surface,  causing  the  rind  to  dry  and 
crack.  While  the  most  noticeable  injury  by  this  mite  occurs  on  the 
fruit,  it  also  occurs  on  and  does  injury  to  the  leaves.  The  leaves  lose 
their  green,  glossy  appearance  and  become  pale  colored  or  silvery  and 
sometimes  curled. 

Formerly  a  special  demand  was  created  for  the  russet  orange  of 
Florida,  which  was  supposed  to  be  sweeter  and  also  possessed  better 
keeping  qualities.  The  injury  that  occurred  on  the  surface,  in  the  case 
of  nearly  mature  fruit  at  any  rate,  apparently  does  not  affect  the  quality 
of  the  interior.  The  market  demands,  however,  a  good  appearing  fruit, 
as  well  as  a  good  tasting  fruit,  and  the  russet  orange  is  not  so  popular  as 
formerly.  Moreover,  such  artificial  injury  to  the  fruit  must  be  shared  to 
some  extent,  at  least,  by  the  foliage,  and  consequently  the  vigor  of  the 
tree  is  more  or  less  impaired.  It  is  of  special  importance,  however,  that 
the  rind  of  the  lemon  appears  bright  and  attractive,  and  thus  " silvered" 
or  " russeted"  lemons  have  found  no  sale  whatever.  When  the  pest  first 
appeared  in  California  the  lemons  were  discarded  as  culls,  but  later  they 
were  utilized  by  the  citric  acid  factory.  There  is  no  longer  any  excuse 
whatever  for  suffering  any  serious  loss  through  the  silver  mite,  though 
the  loss  will  occur  unless  treatment  is  applied  when  the  mite  appears. 

Distribution. — In  California  the  silver  mite  is  restricted  to  a  limited 
section  in  San  Diego  County.  It  was  introduced  here  directly  from 
Florida,  and  never  seems  to  have  become  established  elsewhere.  There 
are  other  citrus  sections  where  the  climate  is  very  similar,  and  there  is 
every  reason  to  suppose  that  it  would  thrive  elsewhere,  particularly  in 
the  coast  sections.  This  is  another  species  that  seems  to  do  best  in 
sections  of  more  or  less  moisture.  In  Florida  it  is  generally  distributed 
throughout  most  of  the  citrus  sections. 

DESCRIPTIONS — LIFE   HISTORY— HABITS. 

The  Egg. — The  egg  of  this  mite  is  white  or  transparent  in  color,  with 
some  showing  a  slight  tinge  of  yellow.  They  are  circular  in  shape  and 
very  minute,  being  scarcely  visible  without  a  magnifier.     Four  or  five 


Bulletin  234]         RED    SPIr)ERS    AND   MITES    OF    CITRUS   TREES.  497 

days  are  required  for  hatching  during  the  summer  months,  and  as  long 
as  ten  days  to  two  weeks  during  the  colder  and  wet  weather  of  winter. 
Our  records  on  the  number  of  eggs  are  fragmentary.  The  maximum 
number  from  one  female  is  fifteen,  but  it  is  possible  that  this  may  be 
exceeded.  However,  from  such  records  as  were  made,  and  from  general 
observations,  fifteen  or  twenty  eggs  seem  to  be  an  average  number. 

The  Young  Mite. — The  first-hatched  mite  is  elongated,  about  three 
times  as  long  as  broad  and  of  a  light  yellow  color.  It  is  thus  much  more 
worm-like  than  any  of  the  other  mites  found  on  citrus  trees.  The  cast 
skins,  which  may  be  seen  on  the  foliage  of  fruit  after  the  mites  them- 
selves have  disappeared,  are  very  minute,  tapering,  or  cornucopia-like 
objects. 

The  Adult. — Even  the  full  grown  mite  is  very  minute,  not  measuring 
more  than  .15  mm  in  length,  which  is  equal  to  about  3/500  of  an  inch, 
The  body  consists  of  two  parts,  the  head  fused  with  the  thorax  and 
known  as  the  cephalothorax,  as  in  other  mites,  and  a  very  much  longer, 
tapering  abdomen,  which  is  made  up  of  a  number  of  rings.  The  head  is 
pointed  and  bent  downwards.  The  rostrum  contains  two  slender  stylets, 
the  mandibles,  which  are  used  for  piercing  the  plant.  On  each  side  of 
the  rostrum  is  a  three-pointed  maxillary  palpus,  and  these  serve  as 
antennas.  The  abdomen  is  cylindrical  and  transversely  striated,  giving 
it  the  appearance  of  being  made  up  of  a  number  of  segments  or  rings. 

On  account  of  the  short  time  required  to  reach  maturity,  eight  to  ten 
days,  these  mites  may  become  very  abundant.  They  have  very  limited 
powers  of  locomotion,  and,  hence,  but  a  portion  of  a  tree  or  a  few  trees 
here  and  there  will  be  found  infested,  rather  than  a  general  distribution 
over  the  whole  grove.  Sometimes  the  evidence  of  injury  is  limited  to 
but  a  few  of  the  fruit. 

For  control  measures  see  page  519. 

Tenuipalpus  californicus   Banks. 

This  is  a  small  species  that  is  somethimes  found  on  citrus  trees  in  con- 
siderable numbers  but  the  actual  evidence  of  injury  is  not  often  appar- 
ent. It  is  a  red  species  of  small  size  that  is  characterized  by  its  flatness. 
They  are  usually  motionless  and  lie  very  flat  upon  the  leaf  or  fruit  and 
look  not  unlike  minute  scales.  This  is  the  only  species  of  the  genus 
Tenuipalpus  recorded  from  the  United  States.  What  appears  to  be 
another  species  has  been  found  on  the  Boston  ivy.  This  one  was  so  abun- 
dant on  ivy  growing  on  the  courthouse  at  Santa  Barbara  as  to  seriously 
injure  it.  The  cast  skins  almost  completely  covered  the  upper  surface 
of  the  leaves  in  many  cases. 

Color,  red.  Body  widest  at  cephalothorax  and  then  suddenly  narrowing,  making 
the  abdomen  appear  more  or  less  cylindrical.  The  margin  of  the  cephalothorax  for  a 
short  distance  is  serrate.  The  body  is  practically  devoid  of  hairs.  From  the  pos- 
terior margin  there  arise  six  lanceolate  leaf-like  appendages  with  serrate  edges. 
These  may  be  called  hairs,  are  are  so  represented  by  Banks,  though  they  are  not  ordi- 


498 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


nary  hairs.  The  palpi  are  small,  and  this  character,  together  with  the  presence  of 
eyes,  distinguish  this  genus  from  Tetranychus.  The  legs  are  short  and  rugose  with 
a  few   minute   scattering    hairs.     The   tarsi   end   in   an   expanded  portion  which   is 


Fig.   8. — Tenuipalpus  californicus  Banks. 

divided  into  four  short  clavate  hairs.     There  also  arise  from  the  tip  of  the  tarsus 
one  long  and  a  few  shorter  hairs. 


Tetranychoides  californicus  Banks. 

This  species  is  sometimes  found  in  immense  numbers  on  citrus  trees. 
It  is  at  once  recognized  by  the  cast  skins  being  confined  to  definite  areas, 


Fig.  9. — Tetranychoides  californicus  Banks. 


usually  on  the  under  surface  of  the  leaf.     Cast  skins  of  sexmaculatus 
are  congregated  in  special  places  also,  but  these  are  always  covered  with 


Bulletin  234]         RED    SPIDERS   AND   MITES    OF    CITRUS   TREES. 


499 


a  web  and  the  leaf  surface  is  of  a  yellowish  color  and  covered  with  black 
specks.  With  Tetranychoides  the  cast  skins  are  arranged  in  a  compact 
mass  and  the  surface  of  the  leaf  is  normal.  They  wander  about  in 
their  feeding  and  seem  to  come  to  definite  headquarters  only  for  the 
purpose  of  molting.  The  injury  done  by  this  species  is  slight  as  com- 
pared with  the  numbers  that  may  be  present. 

This  mite  is  of  a  pale  pink  color,  sometimes  being  almost  white.  Body 
broadest  at  cephalothorax  and  then  narrowing  suddenly.  Length  .22, 
width  .13  mm.  Rostrum  rather  broad  at  tip.  Palpi  long,  five  jointed, 
extending  beyond  rostrum  and  tapering  to  a  point,  the  last  joint  being 
small  and  fiber-like.  The  tarsi  end  in  two  very  slightly  curved  claws 
between  which  is  an  oval-shaped  pad  covered  with  numerous  short  hairs. 


Caligonus  terminalis  Banks. 

This  is  a  red  species  that  has  been  taken  on  citrus  foliage  in  San 
Diego  County,  usually  associated  with  sexmaculatus.  It  will  be  found 
very  often  in  the  colonies  with  this  species  and  seems  to  make  use  of 
the  protective  web  formed  by  the  latter.  It  is  distinctly  red  in  color, 
though  not  as  dark  a  red  as  mytilaspidis.  The  body  surface  is  also 
smooth  and  shiny  instead  of  velvety.  The  eggs  are  red  in  color,  but 
paler  than  mytilaspidis.  They  are  spherical  in  shape  and  without  a 
stalk.  The  numbers  of  this  species  have  never  been  large  and  the  injury 
done  is  not  very  important. 


Fig.  10. — Caligonus  terminalis  Bks.     Palpus  and  tip  or  tarsus. 


Body  red.  Rostrum,  palpi  and  legs  usually  yellow.  Body  surface  smooth  and 
shiny.  Broad  in  middle  and  tapering  toward  both  ends.  Length  .3  mm.  Greatest 
width  .14  mm.  Twenty-six  to  twenty-eight  hairs  clothe  the  dorsal  surface.  These 
are  very  short  and  not  arranged  in  definite  rows  and  do  not  arise  from  tubercles. 


500 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


The  palpi  are  four-jointed,  .11  mm  in  length  and  tapering  toward  the  tip.  The 
thumb  is  very  long,  as  long  or  longer  than  the  claw.  It  extends  out  straight  in  the 
direction  of  the  palpus.  From  the  extreme  tip  there  arises  a  single  finger  and  a 
longer  hair.  The  claw  is  large  and  very  slightly  curved:  Mandibles  rather  sharply 
pointed.  Length  of  fore  leg  .22  mm.  It  is  thus  slightly  shorter  than  the  body. 
Fourth  pair  of  legs  of  same  length,  while  second  and  third  pair  are  somewhat  shorter. 
The  tarsi  end  in  two  distinct  claws  which  are  strongly  curved.  They  are  distinctly 
separated  at  the  base,  and  from  between  them  there  arises  a  projection  which  is  cleft 
into  four  parts. 

Tetranychus  bimaculatus  Harvey. 

This  species  is  only  occasionally  found  on  citrus  trees  and  is  not 
strictly  a  citrus  fruit  species.  Although  it  becomes  very  abundant  on 
several  different  kinds  of  plants  that  may  be  growing  near  or  among 
citrus,  it  is  only  occasionally  that  it  leaves  its  usual  food  plants  for 
citrus  foliage.  Structurally  this  species  is  very  close  to  sexmaculatus. 
The  difference  is  in  the  number  of  fingers  on  the  thumb.  Sexmaculatus 
has  three  fingers  at  the  tip  of  the  thumb  while  bimaculatus  has  but  one 
at  the  tip  and  one  toward  the  base.     But  this  character  seems  to  be 


Fig.  11.— Tetranychus  bimaculatus  Harvey. 

variable,  and  it  is  sometimes  difficult  to  distinguish  the  species  on  this 
alone.  In  the  latter  species  there  is  a  red  form  which  is  very  common 
and  distinct.  In  the  sexmaculatus  that  occurs  on  citrus  trees  this  red 
form  has  never  been  seen.  Sexmaculatus  is  limited  in  its  feeding  to 
definite  areas,  on  the  citrus  tree  at  least,  while  bimaculatus  on  violets, 
beans  and  its'other  common  food  plants  feeds  generally  over  the  entire 
surface.  Bimaculatus  is  the  commonest  species  of  spider  found  in 
southern  California  on  ornamental  shrubs  and  plants  and  on  certain 
vegetables,  as  beans.    The  total  list  of  its  food  plants  is  a  very  long  one. 


Bulletin  234] 


RED    SPIDERS    AND    MITES    OF    CITRUS   TREES. 


501 


In  the  north  central  part  of  the  State  it  is  sometimes  an  important 
pest  on  hops.  It  is  a  species  that  has  been  much  written  about,  and  it 
is  not  necessary  to  characterize  it  in  detail  here. 

Bryobia  pratensis  Garman. 

This  mite  is  known  in  the  East  as  the  clover  mite,  since  it  does  most 
damage  to  clover  and  was  first  described  from  that  plant.  In  this  State 
it  is  better  known  as  the  almond  mite,  for  it  is  most  injurious  to  the 
almond,  and  occurs  throughout  the  coast  valleys  and  in  the  interior 
valleys  from  Red  Bluff  to  Bakersfield,  as  well  as  in  southern  California. 
In  the  citrus  section  it  occurs  chiefly  on  almonds  and  peaches,  and  also 
on  vetch  that  is  grown  in  citrus  groves  as  a  cover  crop.    Although  it 


Fig.  12. — Bryobia  pratensis  Gar. 

occurs  on  vetch  growing  beneath  the  trees  or  on  almonds  growing  in 
the  midst  of  citrus  trees,  we  have  never  taken  it  on  citrus  foliage 
excepting  as  it  may  occur  there  incidentally. 

Bryobia  is  easily  distinguished  from  other  species  because  of  the 
long  fore  legs,  the  four  scale-like  projections  on  the  front  margin  of  the 
cephalothorax,  and  the  scale-like  hairs  on  the  body  itself.  It  is  of  a 
dark  color.  The  winter  is  passed  in  the  egg  stage  and  on  the  twigs  of 
almonds,  prunes,  apricots  and  other  fruits,  these  red  eggs  will  be  found 
in  immense  numbers  oftentimes. 


502 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


Tyroglyphus  americanus  Banks. 

This  is  a  pale  colored  species  that  has  been  taken  from  lemons  in 
storage.    It  belongs  to  the  family  of  Tyroglyphidce,  several  members  of 


Fig.   13. — Tyroglyphus  americanus  Banks. 


which  attack  stored  foods  and  the  roots  and  bulbs  of  living  plants. 
Specimens  have  been  found  swarming  on  lemons  in  an  advanced  stage 


Fig.  14. — Gamasid  sp.     Predaceous. 


Fig.  15. — Gamasid  sp.     Predaceous. 


Bulletin  234]         RED    SPIDERS   AND   MITES    OF    CITRUS   TREES.  503 

of  decay.  There  seems  little  doubt  that  such  mites  are  responsible  for 
the  spread  of  organisms  that  are  responsible  for  decay.  The  commonest 
member  of  the  family  Tyroglyphidce  in  this  country  is  the  mushroom 
mite,  T.  lintneri,  which  is  sometimes  very  destructive  to  cultivated 
mushrooms.  The  cheese  mite,  T.  siro,  is  also  a  related  species.  Our 
species  may  be  distinguished  by  the  description  which  follows: 

Pale  colored ;  body  elongate ;  length,  .4  mm  ;  width,  .22  mm.  Clothed  with  many 
long  hairs.  Some  of  these  at  the  posterior  end  being  about  as  long  as  the  body. 
Altogether  there  are  twelve  on  the  posterior  margin,  two  somewhat  shorter  ones  just 
posterior  to  a  line  through  the  last  coxae,  two  anterior  to  these  and  closer  together,  a 
row  of  six  just  back  of  the  cephalothorax  and  another  row  of  four  on  the  cephalo- 
thorax.  The  line  separating  the  abdomen  from  the  cephalothorax  is  distinct.  The 
tarsi  end  in  a  single  sharply  curved  claw  and  there  is  also  a  circular  pad  or  sucker. 
A  long  hair  arises  from  the  tip  of  each  tibia.  On  tarsi  I  and  II  there  is  the  usual 
clavate  hair  which  is  the  distinguishing  character  of  the  family.  But  on  tarsi  I  there 
is  an  additional  clavate  hair  very  much  smaller  than  the  other  and  nearer  the  tibia 
and  outward  from  the  larger  one.  The  mandibles  are  chelate.  The  palpi  are  very 
small  and  appear  to  arise  from  the  sides  of  the  rostrum.  This  species  is  near  T. 
lintneri,  but  the  arrangement  of  the  hairs  is  different,  the  feathered  ones  are  not 
present  on  legs  I  and  II  and  the  presence  of  the  additional  clavate  hair  on  tarsi  I 
seems  to  make  it  distinct. 

Gamasid  sp. 

This  species  was  associated  with  Tyroglyphus  on  the  stored  lemons 

and  was  present  in  about  equal  numbers.     It  is  a  predaeous  species. 

The  character  distinguishing  it  from  all  other  species  of  mites  taken  on 

citrus  fruits  is  the  presence  of  feathered  hairs  over  the  body.     The 

species  is  characterized  as  follows: 

Pale  colored  body,  oval  in  shape,  slightly  broaded  behind ;  length,  .33  mm,  width. 
.26  mm  ;  fore  legs  equal  to  length  of  body  ;  others  slightly  shorter.  Body  covered 
with  many  short  plumose  hairs.  These  hairs  are  arranged  regularly  in  eight  rows. 
Around  the  base  of  each  hair  is  a  smooth  area  with  a  definite  outline  giving  the  sur- 
face the  appearance  of  being  made  up  of  many  plates.  These  areas  are  of  a  definite 
shape,  many  having  a  constriction,  while  some  appear  to  be  distinctly  double,  the  sep- 
aration being  made  by  the  constriction.  "The  hairs  are  stiff  and  slightly  curved  with 
five  plumose  hairs  arising  from  the  surface.  The  cephalothorax  ends  anteriorly  in  a 
rounded  projection  from  which  arise  two  short  plumose  hairs.  The  palpi  are  large, 
five  jointed,  the  last  joint  bearing  a  divided  claw  near  the  tip  on  the  inner  margin, 
while  several  hairs  arise  from  the  extreme  tip.  The  mandibles  are  long  and  chelate. 
The  mandibular  plate  broad,  with  a  marked  constriction  at  the  center.  The  tarsi  end 
in  an  expanded  portion  from  which  arises  a  circular  pad,  which  is  supported  by  two 
minute  claws  that  extend  at  right  angles  to  the  axis  of  the  tarsus. 

Tarsonemus  approximatus  Bks.  Mss. 

This  is  an  exceedingly  small  mite  that  is  occasionally  met  with  on 
citrus  trees.  It  has  been  taken  from  the  foliage,  and  from  under  scale 
insects.  The  latter  situation  has  aroused  some  suspicion  that  they  may 
be  feeding  on  the  eggs  of  such  scale  insects  as  the  black  and  purple, 
although  the  usual  habits  of  the  group  are  as  vegetable  feeders  and 
some  are  credited  with  doing  considerable  injury  to  grasses,  tea,  pine- 
apples, and  greenhouse  plants.  T.  assimilis  Bks.  Mss.  was  also  taken 
on  citrus. 

A  very  minute  species,  length,  .13  mm ;  width,  .08  mm ;  oval  in  shape  and  devoid 


504 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


of  hairs  excepting  on  the  legs  and  a  few  at  the  tip  of  the  body.  The  rostrum  is  cone 
shaped.  The  palpi  are  inconspicuous  and  closely  oppressed  to  the  sides  of  the 
rostrum.  The  clavate  organ  between  the  first  and  second  pairs  of  legs  is  conspicuous, 
being  very  broad  and  oval-shaped  at  the  tip.  This  clavate  organ  of  unknown  use  is 
the  distinguishing  character  of  the  family  Tarsonemidw.  The  line  separating  the 
cephalothorax  from  the  abdomen  is  fairly  distinct.  The  legs  are  short  and  end  in  two 
minute  claws  and  also  a  pad.     The  fourth  pair  in  the  female  are  more  slender  and 


Tarsonemus  approximatus  Bks.  Mss. 


whip-like,  ending  in  two  long  threads,  one  of  which  is  considerably  longer  than  the 
other.  The  fourth  pair  of  legs  in  the  male  are  very  stout  and  end  in  a  single  large 
curved  claw.  One  or  two  smaller  spines  or  hairs  arise  from  the  base  of  the  claw  on 
the  inner  side,  while  a  very  long  hair  extends  outward.  The  body  of  the  male  is  also 
much  shorter  and  broader  than  that  of  the  female.  The  single  claw  on  the  fourth 
tarsus  of  the  male  distinguishes  it  from  any  of  the  species  figured  in  Banks 
monograph. 

Eremaeus  modestus  Bks. 
This  species  is  one  that  has  not  been  noted  to  affect  the  foliage  or 
fruit  of  the  orange,  but  has  been  seen  in  immense  numbers  on  the  trunk 


Fig.  17. — Eremaeus  modestus. 


and  large  branches.     They  have  the  habit  of  congregating  in  compact 
masses  as  close  as  it  is  possible  for  them  to  pack  together.    Such  masses 


Bulletin  234]         RED    SPIDERS    AND   MITES    OF    CITRUS   TREES.  505 

have  been  seen  to  extend  for  several  feet  up  and  down  the  branches 
and  to  contain  countless  millions  of  mites.  These  were  probably  feed- 
ing on  the  lower  forms  of  plant  life  that  were  growing  on  the  bark  of 
the  tree,  as  certain  forms  of  algae  which  give  a  green  coating  to  the 
bark. 

This  species  belongs  to  the  family  Orbatidce,  or  "beetle  mites,"  so 
called  because  the  body  covering  is  hard  and  coriaceous.  It  is  of  a  dark 
brown  or  black  color  and  pointed  at  the  anterior  end.  Other  species 
of  this  group  have  been  found  in  damp  situations  such  as  on  flower 
pots  that  have  been  kept  in  the  ground.  The  species  mentioned  above 
was  found  on  large  trees  that  afforded  plenty  of  shade  and  it  was  also 
during  the  winter  season. 

Key  to  the  Species  of  Red  Spiders  and  Mites  recorded  in  this  Bulletin. 

(Partially  adapted  from  Banks.) 

\     1.  Abdomen  annulate ;  minute  form     .         .     Silver  mite,  Eriophyes  oleivorus 

)     2.  Abdomen  not  annulate 3 

\     3.  Body  coriaceous         .......         Eraemus  modestus 

I     4.  Body  not  coriaceous 5 

\     5.  With  clavate  organ  between  legs  I  and  II  in  the  female     Torsonemus  sps. 

\     6.  Without  such  clavate  organ 7 

(     7.  With  clavate  hair  on  tarsi  I  and  II         .         .         Tyroglyphus  americanus 

/     8.  Without  such  clavate  hair       .........  9 

\     9.  Front  legs  twice  as  long  as  the  body     ....     Bryooia  pratensis 

I  10.  Front  legs  not  twice  as  long  as  body         .......     11 

\  11.  Palpi  ending  in  a  distinct  thumb  and  with  claw 17 

/  12.  Palpi  without  thumb  and  claw 13 

13.  Mandibles  chelate      ........         Gamasid  sps. 

14.  Mandibles  not  chelate 15 

f  15.  Palpi  very  small,  legs  short,  rugose         .         .         Tenuipalpus  californicus 

4    16.  Palpi  rather  long  and  slender,  legs  longer  and  not  rugose 

Tetranychoides  californicus 

\  17.  Bristles  of  body  arising  from  tubercles         .         Tetranychus  mytalispidis 

I  18.  Bristles  of  body  not  arising  from  tubercles         .         .         .         .         .         .17 

f  19.  Tarsus  with  two  claws         .....         Caligonus  terminalis 

|  20.  Tarsus  with  but  one  claw 19 

I  21.  With  three  fingers  at  tip  of  thumb,  color  never  red 

[  Tetranychus  sexmaculatus 

\   22.  With  one  finger  at  tip  of  thumb  and  one  nearer  base.     Red  forms 

/  often  occurring         .....         Tetranychus  oimaculatus 

NATURAL   ENEMIES. 

Red  spiders  and  mites,  exposed  as  they  are  throughout  their  lives  on 
the  surface  of  the  leaves  or  fruit,  are  subject  to  the  attacks  of  a  consid- 
erable number  of  enemies.  But  in  the  course  of  our  investigation  the 
number  has  not  been  so  striking  as  the  unusual  variety  of  their  enemies. 
We  commonly  think  of  thrips  as  plant  enemies  rather  than  predaceous 
insects.  Members  of  the  family  Itonidce  (C ecidomyiidce)  are  better 
known  on  account  of  their  gall-making  habits  and  attacks  on  living 
plants  rather  than  as  parasites.  Most  of  the  Staphylinid  beetles  feed 
on  decaying  vegetable  and  animal  matter,  while  a  much  smaller  number 


506  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

are  known  to  be  predaceous.  "While  all  members  of  the  family  Coniop- 
terigidce  are  predaceous,  they  are  such  rare  insects  and  so  little  known 
about  them  that  they  are  no  less  interesting  than  the  others  mentioned. 
Aside  from  these,  there  a^e  the  usual  Coccinellids,  Hemerobiids,  Cryso- 
pids,  and  mites,  and  as  a  hyper-parasite,  a  chalcid.  The  natural  ene- 
mies of  our  citrus  spiders  thus  include  the  classes,  Acarina  and  Insecta, 
and  in  the  latter  class  the  following  orders :  Nearoptera,  Thysanoptera, 
Coleoptera,  Diptera,  and  to  include  the  hyper-parasite,  the  Hymen- 
opt  era. 

While  many  of  the  following  predaceous  insects  were  found  feeding 
on  the  six-spotted  mite  and  others,  most  of  the  observations  were  made 
on  the  citrus  red  spider,  and  the  following  statements  have  reference  to 
this  species. 

Conventzia  hageni  Banks. 

This  species  is  one  of  the  commonest  enemies  of  spiders  of  citrus  trees 
in  the  southern  California  citrus  sections.  It  belongs  to  the  family 
Coniopterygidce  of  the  order  Neuroptera.  These  include  the  smallest 
insects  of  the  order.  There  are  also  very  few  representations  of  the 
family  in  the  country  and  only  two  species  in  California.  They  are 
related  to  the  Hemerobiids  and  Crysopids.  The  above  species  feeds  on 
the  red  spider,  both  in  the  larval  and  adult  stages. 

LIFE  HISTORY  AND  HABITS. 

The  Egg. — The  egg  is  pinkish  yellow  in  color  and  oval  in  shape, 
measuring  .5  mm  long  and  .23  mm  wide.     The  surface  is  marked  with 


Fig.    18. — Conventzia    hageni    Banks.     FJggs,    larva, 
pupa.     Feeds  on  Red  Spiders. 

hexagonal  reticulations.  The  eggs  are  deposited  singly,  usually  on  the 
under  surface  of  the  leaf.  Prom  six  to  eight  days  are  required  for  the 
egg  to  hatch. 


Bulletin  234]         RED    SPIDERS   AND   MITES    OF    CITRUS   TREES. 


507 


The  Larva. — The  body  of  the  larva  is  broad  at  the  anterior  end, 
becoming  still  wider  at  the  thorax  and  then  gradually  tapering  toward 
the  posterior  end.     The  color  and  markings  vary  considerably,  but  the 


Fig.  19. — Conventzia  hageni   Banks. 

usual  colors  are  white,  red,  and  black.  The  white  is  present  along  the 
margins,  and  it  also  extends  inward  in  variable  blotches  on  each  of  the 
segments.     There  is  also  a  more  or  less  regular  line  of  white  on  the 


Fig.  20. — Conventzia  hageni  Banks.     Mouthparts  of  larva  on  left. 
Mouthparts  of  adult  on  right. 

median  dorsal  line.  The  antennae  consist  of  one  short  and  one  long 
joint,  both  clothed  with  hairs.  The  mouth  parts  consist  of  a  cone- 
shaped  beak  enclosing  the  needle-like  mandible  and  maxillae,  the  latter 
being  serrate  at  the  tip.     The  palpi  are  broad,  spatula-shaped  append- 


508 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


ages  that  extend  out  on  either  side  like  two  large  ears.     From  the  blunt 
ends  of  the  tarsi  there  arise  two  curved  spurs. 

The  larva  undergoes  three  molts  during  its  period  of  development, 
which  require  an  average  of  fifteen  days.  The  first  molt  occurs  four 
days  after  hatching,  the  second  ten  days  after  hatching,  and  the  third 
on  the  fourteenth  or  fifteenth  day.  Six  days  later  it  begins  to  spin  its 
cocoon  so  that  the  total  larval  period  is  from  eighteen  to  twenty-two 
days. 

The  larva  feeds  on  all  stages  of  the  spider,  including  eggs,  young  and 
adult.  In  attacking  the  eggs  the  mandibles  are  thrust  through  the  egg 
membranes  on  the  lower  side  near  where  it  is  resting  on  the  surface. 
The  entire  contents  are  thus  consumed  generally  from  a  single  puncture. 
The  egg  is  changed  from  a  bright  red  or  pink  color  to  a  transparent 
shell.  Ten  or  fifteen  seconds  is  sufficient  time  for  an  egg  to  be  con- 
sumed. The  contents  of  the  spiders  themselves  are  similarly  absorbed, 
except  that  it  requires  a  longer  time  and  the  puncture  is  not  always 
made  low  down.  From  four  to  seven  minutes  are  required  for  taking 
out  the  body  contents  of  the  larger  spiders.  These  are  reduced  to  a 
small  crumpled  mass  with  a  small  amount  of  the  red  pigment  still 
present. 

The  capacity  of  the  Coniopteryx  larva  for  feeding  is  shown  in  the 
table  below.  From  this  it  will  be  seen  that  one  larva  consumed  96 
spiders  in  sixteen  days;  another  a  total  of  226  spiders  for  its  develop- 
ment from  hatching  to  pupation;  another  136  in  eleven  days;  another 
253  for  its  whole  larval  period ;  and  another  (not  in  the  table)  53  spiders 
in  three  days. 

Conventzia  hageni  Banks. 

Feeding  of  Larva. 


Spiders  consumed. 

-a 

3 

H3 

o 
pa 

> 

--• 

CO 

H 

M 

M 

M 

M 

M 

M 

e» 

Larva    No. 

K> 

a 

a 

& 

C3- 

&■ 

E? 

& 

£ 

o 

CO 

B 

>** 

& 

& 

& 

E? 

a 

SO 

& 

a 

a 

a 

& 

a 

& 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

a 

■a 

]3 

<< 

vj 

vj 

V3 

vj 

VI 

<« 

VJ 

» 

V] 

VI 

? 

VJ 

VI 

V) 

r 

V] 

V4 

! 

** 

1 

3 

20 
2 

5 

9 

25 
13 

12 
15 

m 
25 
25 

13 
m 

15 

16 

9 

19 
25 
m 

25 
25 
25 

25 

25 

25 

25 

25 

226 
136 
262 

1 
16 
11  i 

18  | 

15 

9 

12 

O 

—- 

m 

25 

25 

25 

25 

25 

25 

23 

15 

Pupation  and  the  Cocoon.— When  fully  mature  the  larva  selects  a 
place  on  the  under  side  of  the  leaf,  usually  along  the  midrib,  but 
occasionally  on  other  parts  of  the  leaf  where  there  is  some  little  pro- 
tection. Where  the  six-spotted  mite  is  attacked  the  depressions  formed 
by  this  species  are  a  very  common  place  chosen.  The  thread  is  emitted 
at  the  posterior  end  and  the  movements  in  spinning  the  web  describe  a 
figure  8. 


Bulletin  234]         RED    SPIDERS    AND   MITES    OF    CITKUS   TREES.  509 

The  cocoon  consists  of  a  double  layer  of  silk,  an  inner  compact  layer 
more  or  less  oval  in  shape  and  an  outer  flat,  loosely  woven  web.  This 
outer  covering  extends  out  beyond  the  inner  cocoon  and  makes  it  appear 
very  flat  on  the  leaf.  These  cocoons  are  nearly  always  to  be  found  on 
the  under  side  of  the  leaf  and  they  look  not  unlike  the  masses  of  Psocid 
eggs  with  their  silken  covering,  or  like  some  of  the  masses  of  the  smaller 
spiders '  eggs.  The  diameter  is  about  6  mm,  and  an  examination  for  the 
double  layer  of  silk  will  at  once  distinguish  the  cocoons  of  this  insect. 

The  Pupa. — The  pupa  is  of  a  reddish  brown  color.  The  head  is 
deflexed  and  the  appendages  lie  fairly  close  to  the  ventral  surface.  The 
time  spent  in  the  pupal  stage  is  thirteen  days,  the  period  varying  but  a 
day  or  two  from  this  on  all  of  which  records  were  made. 

The  Adult. — When  the  transformation  to  the  adult  occurs  within  the 
cocoon  the  insect  emerges  by  pushing  out  on  its  side  usually  through  the 
outer  cocoon,  at  the  same  time  splitting  the  inner  cocoon.  When  partly 
out,  after  resting  for  a  short  period,  it  crawls  out  by  pulling  itself  along 
with  its  legs,  which  by  this  time  are  freed. 

The  mature  insect  is  a  small,  very  frail  insect,  about  one  fifth  of  an 
inch  long  and  of  a  grayish  white  color.  The  wings  are  covered  with  a 
grayish  powder  and  members  of  this  group  are  called  dusty  wings.  The 
second  pair  of  wings  are  very  small  as  compared  with  the  fore  wings. 
The  antennae  are  long  and  beadlike,  consisting  of  many  joints.  There 
are  a  pair  of  five-jointed  and  a  pair  of  three-jointed  palpi  arising  from 
the  mouth.  The  tarsi  are  made  up  of  five  joints,  the  third  being  very 
short  and  broad. 

Oligota  oviformis  Casey.* 

This  species  is  one  of  the  Staphylinidce  or  rove  beetles.  According  to 
Dr.  Fenyes  it  is  taken  occasionally  from  the  flowers  of  the  Christmas 
berry,  and  also  from  the  leaves  of  the  live  oak,  where  it  probably  feeds 
on  small  Arthropods.  We  have  found  the  species  feeding  on  the  red 
spider  in  both  the  larval  and  adult  stages.  They  were  taken  on  citrus 
trees  from  Los  Angeles  to  San  Diego,  sometimes  occurring  in  large  num- 
bers. March,  April,  May  and  June  were  the  months  when  they  were 
most  common.  The  larva  is  long  and  slender  and  the  adult  is  a  pecu- 
liarly shaped  black  beetle  with  the  head  pointing  downward  and  the  tip 
of  the  abdomen  sticking  upward. 

DESCRIPTIONS — LIFE  HISTORY — HABITS. 

The  Egg. — The  egg  is  of  a  light  orange  color,  oval  in  shape  and  with  a 
slightly  reticulate  surface.  The  length  is  .36  mm  and  the  width  .25  mm. 
They  are  laid  singly  on  the  under  surface  of  the  leaf.  Hatching  occurs 
in  seven  to  nine  days. 

*Casey,  Ann.  N.  Y.  Ac.  Sc.  VII,  p.  381,  1893.     Described  as  Somatium  oviforme. 


510 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


The  Larva. — The  length  of  the  full  grown  larva  is  about  2.5  mm  and 
the  width  .6  mm.  It  is  narrower  at  anterior  end  and  widens  posteriorly ; 
color  yellow.  The  clothing  consists  of  hairs  scattered  about  in  a  more 
or  less  irregular  manner,  but  on  the  abdominal  segments  there  is  a 
definite  row  on  each.  The  antennas  consist  of  three  joints,  the  middle 
joint  being  longest  with  a  prominent  finger  on  the  outer  shoulder.  The 
last  joint  is  much  narrower  than  the  preceding  and  ends  in  a  straight 
spine.  Three  long  hairs  arise  from  the  tip  of  segments  2  and  3.  The 
maxillary  palpi  consist  of  three  joints  which  taper  to  a  point.  The 
labial  palpi  are  similar  in  shape  but  much  shorter.     The  mandibles  are 


Fig.  21. — Oligota  oviformis  Csy.  Larva 
and  adult.  Characteristic  position  of 
adult  shown  below. 


sharp-pointed  and  curved.     From  each  of  the  tarsi  there  arises  a  single, 
very  slightly  curved,  rather  long  claw. 

Manner  of  and  Capacity  for  Feeding. — With  its  sharp  pointed  man- 
dibles the  larva  punctures  the  spider  usually  about  the  center  of  the 
body,  and  by  a  pump -like  action  the  body  content  is  sucked  up.  This 
is  colored  red  and  may  be  distinctly  observed  passing  from  the  body  of 
the  spider  into  the  alimentary  canal  of  the  more  or  less  transparent 
larva  of  Oligota.  As  most  of  the  body  juices  of  the  spider  were  absorbed 
they  were  spewed  back  again,  and  the  spider,  which  had  been  made 
transparent  by  the  absorption  of  the  body  contents,  resumed  its  normal 
color  and  rigidity.     This  pumping  back  and  forth  is  repeated  two  or 


Bulletin  234]         RED    SPIDERS    AND   MITES    OF    CITRUS   TREES.  511 

three  times  before  the  mouth  parts  finally  release  the  victim.  Feeding 
also  occurs  on  the  eggs  in  a  similar  manner. 

The  capacity  of  the  Oligota  larva  for  feeding  is  considerable,  as  our 
records  show  an  average  of  about  twenty  spiders  consumed  each  day. 
This,  too,  includes  a  majority  of  the  more  fully  mature  spiders  since 
they  were  transferred  daily  and  consequently  the  eggs  and  small  spiders 
would  be  left.  Twelve  to  fifteen  days  represent  the  longest  period  we 
have  been  able  to  get  the  larva  to  live.  That  is,  repeated  efforts  have 
failed  to  bring  it  to  the  pupal  stage,  although  our  maximum  records 
carried  them  to  a  stage  just  preceding  pupation.  But  counting  the  time 
that  has  actually  been  observed,  the  larva  will  consume  upwards  of  two 
hundred  or  three  hundred  spiders  during  the  course  of  its  development. 

The  Adult. — The  adult  Oligota  is  a  small  black  peculiarly-shaped 
beetle  with  short  wing  covers  and  with  the  abdomen  strongly  curved 
upward.  The  head  is  bent  under  and  vertical  and  not  visible  from 
above.  The  antennae  are  yellow  and  consist  of  ten  segments.  Are 
club  shaped  with  first  two  joints  longest,  next  five  short  and  small,  while 
the  last  three  are  much  broader  and  bead  shaped.  The  abdomen  is 
pointed.    Body  densely  clothed  with  hairs.    Length  1  mm,  width  .57  mm. 

While  the  adult  of  this  species  does  not  eat  so  many  spiders  each  day 
as  the  larva,  the  longer  life  of  the  adult  makes  the  total  number  con- 
sumed about  equal.  The  adults  require  about  ten  spiders  a  day  and 
the  maximum  adult  life  determined  was  thirty-two  days,  making  a  total 
of  320  spiders  consumed.  A  pair  of  beetles  were  placed  in  a  cell  on 
March  19th  and  furnished  with  spiders  for  food.  Qn  March  22d  egg 
laying  was  begun  and  the  first  larva  hatched  on  April  1st.  There  were 
but  four  larvae  hatched  in  all  and  these  lived  fourteen  days.  The  last 
adult  died  on  May  2d.  The  total  number  of  spiders  consumed  in  this 
experiment  was  792. 

Stethorus  picipes  Csy. 
This  species  was  the  commonest  coccinellid  or  lady  beetle  that  was 
found  to  feed  on  the  red  spider.  It  was  generally  distributed  over  the 
citrus  section,  having  been  taken  in  Los  Angeles,  Orange,  Riverside, 
San  Bernardino,  and  San  Diego  counties.  It  was  most  abundant  of  all 
the  enemies  in  Riverside  and  San  Bernardino  counties. 

DESCRIPTIONS — LIFE    HISTORY — HABITS. 

The  Egg. — The  egg  of  this  coccinellid  is  oval  in  shape  and  pinkish 
yellow  in  color  when  first  deposited,  but  as  hatching  time  approaches  it 
turns  black  or  dark  gray.  The  surface  is  marked  with  hexagonal  retic- 
ulations. The  eggs  are  deposited  singly,  usually  on  the  under  surface 
of  the  leaf.  The  total  number  of  eggs  deposited  of  which  we  have  cer- 
tain records  is  21,  though  this  number  may  be  exceeded  under  perfectly 
3—234 


512 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


natural  conditions.  The  hatching  period  is  seven  or  eight  days  during 
the  month  of  April. 

The  Larva. — The  length  of  the  larva  is  1.  mm  (1/25  of  an  inch)  and 
the  width  .55  mm.  The  color  is  dark  gray  to  black.  The  body  is 
clothed  with  numerous  hairs  arising  from  small  tubercles.  In  addition 
to  these  longer  hairs  the  entire  surface  is  covered  with  short  spines, 
those  along  the  folds  of  the  skin  being  larger  and  darker  in  color. 

The  young  larva  emerges  from  a  longitudinal  rent  in  the  eggshell. 
It  is  at  this  time  of  a  mottled  grayish  yellow  and  black  color.  A  larva 
that  hatched  on  March  1st  molted  on  the  7th  and  20th  and  pupated  on 
the  30th,  making  the  total  larval  life  thirty  days.  Another  hatched  on 
May  1st,  molted  on  the  8th  and  13th  and  pupated  on  the  23d,  a  total  of 
twenty-three  days.     These,  together  with  other  records,  give  the  length 


Pig.   22. — Stethorus  picipes  Csy.     Larva, 
pupa,  adult.     Feeds  on  Red  Spider. 

of  minimum  larval  development  as  twenty-one  days  and  the  maximum 
thirty  days. 

Feeding  records  show  that,  in  the  case  of  one  larva  that  lived  thirty 
days  it  consumed  a  total  of  189  spiders,  or  an  average  of  6  or  7  per  day. 
Another  larva  devoured  a  total  of  110  spiders  in  thirteen  days  or  an 
average  of  8+  per  day.  Records  on  this  larva  were  made  during  the 
latter  half  of  the  development  period. 

The  Pupa.— Pupation  occurs  on  the  under  side  of  the  leaves,  the 
pupa  being  dark  colored,  about  1/20  of  an  inch  long,  and  of  the  usual 


Bulletin  234] 


RED    SPIDERS    AND    MITES    OF    CITRUS   TREES. 


513 


coccinellid  appearance.     One  pupated  March  16th,  emerged  March  21st. 
Another  pupated  April  10th  and  emerged  April  17th. 

The  Adult. — The  adult  is  a  polished  black  beetle  clothed  with  fine  hairs 
and  about  1/20  to  1/25  of  an  inch  long.  The  antennae  are  eleven  jointed, 
with  the  last  three  joints  of  the  small  club  equal  in  length.  The  original 
description  of  this  beetle  will  be  found  in  the  Jour.  N.  Y.  Ent.  Soc, 
volume  VII,  page  136. 


THRIPS. 

(Scolothrips  sexmaculatus  Pergande.) 

Most  species  of  thrips  are  plant  feeders,  and  there  are  several  species 
occurring  in  the  State  that  are  important  pests.  There  are,  however,  a 
few  species  that  are  known  to  be  carnivorous,  though  the  records  on  such 
habits  are  very  fragmentary,  with  the  exception  of  the  above  species, 
which  has  been  observed  by  Pergande  and  Bruner  to  feed  upon  red 
spiders  and  mites.  We  have  repeatedly  observed  the  above  species  to 
feed  on  the  citrus  red  spider.  It  occurred  most  abundantly  during  the 
winter  and  early  spring.     For  the  most  part  the  eggs  and  younger 


Fig.  23. — Scolothrips  sexmaculatus  Perg. 
Feeds  on  Red  Spider. 

spiders  are  attacked,  though  occasionally  the  fully  mature  spiders  are 
eaten.  The  time  required  to  consume  the  contents  of  eggs  and  spiders 
varied  from  three  to  seven  or  eight  minutes.  Most  of  the  contents  of 
the  egg  were  taken  from  a  single  puncture,  then  two  or  three  additional 
punctures  would  be  made  on  different  sides  and  close  to  the  bottom,  to 
get  what  little  of  the  contents  remained.  The  eggs  were  thus  rendered 
perfectly  transparent,  nothing  but  the  shell  remaining. 

In  the  case  of  the  spiders  themselves,  after  taking  most  of  the  body 
contents,  the  spider  would  be  rolled  around  and  punctured  from  differ- 
ent sides,  the  revolving  being  done  by  the  fore  legs  of  the  thrips.  The 
spiders  were  attacked  mostly  before  the  first  or  second  molt,  and  usually 


514 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


at  a  time  when  the  spider  was  in  a  quiescent  stage  just  preliminary  to 
the  molting  process.  In  coming  in  contact  with  the  largest  spiders  the 
thrips  would  sometimes  quickly  retreat,  and  in  one  case  it  was  observed 
to  assume  the  attitude  of  the  praying  mantis,  with  the  fore  part  of  the 
body  elevated  and  fore  feet  extending  downward  from  knee.  In  a  few 
eases,  however,  the  adult  thrips  have  been  seen  to  attack  a  full-grown 
female  of  T.  mytilaspidis.  One  of  these  requires  one  hour  and  ten  min- 
utes to  suck  out  all  of  the  body  contents.  All  stages  of  the  thrips, 
barring  the  pupa,  have  been  noted  to  feed  on  the  red  spider. 

The  general  color  of  this  species  of  thrips  is  pale  yellow,  with  three 
light  brown  spots  on  the  fore  wings.  The  antennas  are  eight  jointed,  the 
sixth  joint  being  the  longest.  The  first  and  second  joints  are  light 
colored  while  the  others  are  dusky  gray. 

Arthrocnodax  occidentalis  Felt  MMS. 

This  is  a  species  of  Itonidae  (Cecidomyiidce),  the  larva  of  which  has 
been  found  to  feed  on  the  red  spider.  This  enemy  of  the  spider  was 
taken  in  widely  separated  localities,  as  Whittier  and  San  Diego,  and 


Fig.  24. — Larva  and  adult  of  Arthroconodax 
occidentalis  Felt  MMS.  Feeds  on  Red 
Spiders. 

appears  to  be  very  generally  distributed.  It  has  been  observed  to  feed 
on  mytilaspidis,  bimacidatus,  and  sexmaculatus.  On  the  last  species  it 
was  taken  in  considerable  numbers  in  San  Diego  County.  The  definite 
colonies,  together  with  their  protective  covering  of  web  that  characterizes 
sexmaculatus,  seem  to  offer  the  best  conditions  for  this  dipterous  larva. 


Bulletin  234]         RED   SPIDERS   AND   MITES    OF    CITRUS   TREES.  515 

Not  having  great  powers  of  locomotion,  it  finds  the  spiders  massed  in  a 
colony  decidedly  to  its  advantage  in  the  capture  of  food,  and,  as  shown 
later,  since  it  is  subject  to  the  attacks  of  a  parasite  the  covering  of  web 
serves  to  protect  it  from  such  attacks. 

The  following  description  will  enable  the  larva  of  this  predatory  Ceci- 
domyid  to  be  identified:  Length  2.2  mm,  width,  .43  mm,  color  yellow. 
Head  end  narrow,  ending  in  a  pair  of  two-jointed  palpi  or  antennae. 
The  first  joint  is  very  broad  and  short  and  should  scarcely  be  called  a 
joint,  though  two-jointed  palpi  are  a  family  characteristic  according  to 
Williston.  The  second  joint  is  straight  and  spine  like.  There  are 
fourteen  body  segments  and  on  the  fifth  to  the  thirteenth,  inclusive,  are 
a  pair  of  nipple-like  stigmata.  Extending  around  each  segment  is  a 
row  of  short  spines  and  on  the  last  segment  are  two  curved  spines.  In 
the  earlier  larval  stages  there  are  three  pairs  of  caudal  spines,  one  small 


Fig.   25. — Parasite  of  Arthrocnodax. 

pair  in  the  center,  which  is  the  pair  that  evidently  persists  in  the  last 
larval  stage,  and  a  much  larger  pair  on  either  side. 

Where  the  number  of  these  larvae  is  large  their  effect  on  checking  the 
spider  is  considerable.  One  on  which  records  were  kept  consumed  165 
spiders  during  a  period  of  fifteen  days.  Another  had  380  spiders  to  its 
credit  during  a  period  of  seventeen  days. 

The  egg  is  long,  narrow,  and  sickle  shaped  and  of  a  brownish  yellow 
color.  Length  .26  mm.  They  are  laid  singly  on  the  under  side  of  the 
leaves. 

The  cocoon  is  spun  on  the  surface  of  the  leaf,  usually  on  the  under 
side.  It  is  a  rather  flat,  oval,  compact  mass  of  silk.  Upon  emerging  the 
pupal  skin  is  left  protruding  nearly  its  full  length  from  the  cocoon. 

The  species  was  sent  to  Dr.  Felt,  of  New  York,  who  identified  it  as 
probably  a  new  species  of  Arthrocnodax,  and  has  since  described  it  as 
Arthrocnodax  occidentalis. 


516 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


Thriphleps  insidiosus  Say. 

This  is  a  carnivorous  bug  belonging  to  the  family  Anthocoridce.  With 
its  large  beak  or  proboscis  which  is  thrust  into  the  spiders,  the  body  con- 
tents are  soon  consumed.  Both  the  nymphs  and  adults  feed  on  the 
spiders.  This  species  was  not  at  all  common  during  the  past  year  and 
therefore  was  of  little  aid  in  checking  the  spiders.  If  its  numbers  were 
large  a  great  many  spiders  would  be  devoured  for  its  capacity  for  feed- 
ing is  considerable.  The  species  may  be  identified  from  the  figures.  It 
is  a  small  bug,  one  twelfth  of  an  inch  long  and  of  a  black  color. 


Fig.  26. — Thriphleps  insidiosus.     Feeds  on  Red  Spiders. 
The  Brown  Lacewing. 

The  larva  of  this  species  is  very  voracious  and  eats  a  large  number  of 
spiders  during  its  development.  Unlike  many  of  the  other  enemies, 
however,  it  is  not  restricted  in  its  feeding  to  spiders  and  mites.  Records 
on  the  feeding  of  two  of  the  brown  lacewing  larva  are  given  below. 


CO 

Hatched. 

Spiders  provided  for  food. 

H3 

o 
p 

> 

-i 
P 

p 
1 

CO 

pi 

P 
«1 

to 

ft 

ft- 

ft 
ft 

B 
& 

B 

& 

89 

V) 

B 
ft 
<< 

-3 

B 
ft 
p 
<<t 

i 

00 

B 

ft 

CO 

B 
ft 

o 

B 

a. 

? 

to 

B 

ft 

? 

ft 
? 

E? 
ft 
P 
<< 

m 

ft 
p 
•< 

ft 
p 
v« 

~3 

B 

18th,  19th 

and  20th 

days. 

^p 

■      CD 

!  « 
!  "■• 

1 

2 

April  4  ___ 
April  4  ... 

25 
25 

22 
25 

25 

47 

25 
25 

25 
50 

50 
50 

50 
50 

50 
50 

50 

50 

50 

42 

35 

8 

50 
50 

50 
100 

100 
100 

escaped 
300  dead 

532 

S97 

31 
44 

This  gives  a  total  of  532  spiders  consumed  in  seventeen  days,  when  it 
escaped,  for  one  larva,  and  a  total  of  897  in  twenty  days  for  the  other, 
when  it  died,  although  this  one  was  no  doubt  mature  and  ready  for  pupa- 
tion. The  spiders  are  caught  and  impaled  on  its  long  lance-like  man- 
dibles and  the  body  contents  absorbed. 


Bulletin  234]         RED    SPIDEKS    AND   MITES    0F    CITRUS   TREES. 


517 


The  egg  of  this  laeewing  is  ovoid  in  shape,  .84  mm  long  and  white  in 
color.  The  surface  is  marked  with  spiral  reticulations,  and  at  one  end 
is  the  small  knob-like  micropyle.  The  eggs  are  laid  singly  on  the  under 
surface  of  the  leaf. 

The  larva  has  the  typical  appearance  of  Chrysopa  or  Hemerobius 
larva  with  its  large  sword-like  mouth  parts.  While  Hemerobiid  larvae 
have  been  given  certain  general  characters,  such  as  width  of  head  and 
shape  of  body,  that  distinguishes  them  from  Chrysopa  larvae,  this  is  not 
sufficient  to  warrant  a  positive  determination.  In  such  literature  as  we 
have  at  hand  there  are  certain  structures  on  the  feet  of  Chrysopidce  that 
are  described  as  peculiar  to  this  family.  This  structure  is  a  very  prom- 
inent, trumpet  or  elongate  bell-shaped  sucker,  situated  between  the  claws. 
But  we  find  this  present  also  on  the  feet  of  the  larva  of  the  brown  lace- 
wing,  so  that  it  is  not  limited  to  the  Chrysopidce  alone.  The  antennae 
of  the  brown  laeewing  larva  are  composed  of  three  joints  and  the  whole 
is  distinctly  annulate.     The  rings  are  very  close  together  and  each  is  not 


Fig.    27. 


-Brown    Laeewing.     Hemerobius    pacificus    Banks. 
Feeds   on   Red   Spider. 


distinct  so  that  several  cross  lines  occur  connecting  the  different  rings. 
In  the  larva  of  the  Chrysopa  which  has  been  associated  with  the  brown 
laeewing  on  citrus  trees,  the  antenna  is  not  made  up  of  three  distinct 
joints.  There  is  a  short,  broad,  basal  joint  similar  to  the  corresponding 
one  in  the  brown  laeewing.  At  about  two  thirds  of  the  way  to  the  tip 
there  is  in  the  Chrysopa  a  distinct  shoulder  where  the  antennae  suddenly 
narrow.  Arising  from  this  shoulder,  which  is  probably  a  sensory  pit, 
there  is  a  short  stout  spine.  But  there  is  no  evidence  of  a  distinct  joint, 
and  the  outer  surface  at  this  point  is  not  interrupted.  In  Chrysopa  the 
basal  part  is  made  up  of  rings  that  are  distinctly  farther  apart  than 
those  more  distal.  Indeed  these  longer  rings  on  the  basal  half  of  the 
antennae  of  Chrysopa  are,  in  the  two  species  concerned,  the  most  prom- 
inent distinguishing  characters. 


518  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

The  cocoon  consists  of  a  very  thin,  loosely  woven  layer  of  silk  which  is 
formed  on  the  leaf  surface,  usually  the  under  side.  The  cocoon  is,  thus, 
very  different  from  its  ally  the  Chrysopa,  which  consists  of  a  very 
definite  and  compact  cocoon. 

The  adult  of  this  species  is  distinctly  brown  in  color  and  about  two 
fifths  of  an  inch  long  to  the  tips  of  the  wings.  The  antennae  are  made 
up  of  numerous  bead-like  joints.  The  entire  insect  is  clothed  with  short 
brown  hairs.  The  life  cycle  requires  about  fifty  days.  The  egg  stage 
lasts  about  eight  days,  the  larval  life  is  twenty  days  and  twenty  days  are 
spent  in  the  cocoon. 

The  Green  Lacewing. 

This  is  the  commonest  of  the  predatory  insects  occurring  on  citrus 
trees.  The  larva  resembles  very  much  that  of  the  preceding  species, 
except  the  distinctions  noted,  and  the  fact  that  it  is  considerably  larger. 
The  eggs  are  the  familiar  stalked  ones  that  may  be  seen  extending  out 
from  the  twigs  or  surface  of  the  leaves.  This  is  a  provision  to  prevent 
those  larvae  first  hatching  from  devouring  the  eggs  not  yet  hatched,  since 
they  are  strongly  cannibalistic.     This  precaution  is  not  followed,  how- 


Fig.  28. — Green  Lacewing,  Chrysopa  calif ornica  Coq.     Feeds  on  Red  Spider 


ever,  in  the  case  of  the  brown  lacewing.  The  feeding  habits  of  both  of 
these  species  are  much  the  same,  and  consequently  need  not  be  repeated. 
-  The  cocoon  is  formed  on  the  leaf  and  consists  of  a  very  compact  layer 
of  closely  woven  silk  with  a  more  or  less  irregular  loose  covering  on  the 
outside  to  hold  it  in  place.  It  is  oval  in  shape  with  the  long  axis  extend- 
ing vertically  from  the  leaf.  When  ready  to  emerge  the  adult  cuts  a 
very  even  line  almost  around  the  upper  third,  leaving  just  enough  to 
serve  as  a  hinge  for  the  cap  that  is  pushed  back  as  it  emerges. 

The  adult  is  larger  than  the  brown  lacewing,  measuring  about  three 
fifths  of  an  inch  to  the  tips  of  the  wings.  It  is  distinctly  green  in  color 
with  delicate  iridescent  wings.     Its  larger  size,  absence  of  the  clothing 


Bulletin  234]         RED    SPIr)ERS   AND   MITES    OF    CITRUS   TREES.  519 

of  hairs,  and  the  cylindrical,  rather  than  beaded  joints  of  the  antennae, 
will  at  once  distinguish  the  adult  of  the  green  from  that  of  the  brown 
lacewing. 

Other  Enemies. 

Aside  from  those  enemies  mentioned,  there  are  some  of  the  native 
Coccinellids  that  feed  to  some  extent  on  red  spiders.  Probably  the  com- 
monest one  seen  during  the  last  couple  of  years  has  been  Olla  abdomin- 
alis.  There  are  also  two  or  three  species  of  Syrphus  fly  larva  that  eat 
red  spiders.  Among  the  mites  there  have  been  noted  four  or  five  preda- 
tory ones.  One  of  these,  Fig.  15,  was  taken  very  generally  over  the 
citrus  section  but  always  in  scattering  numbers. 

THE  CONTROL  OF  SPIDERS  AND  MITES  ON  CITRUS  TREES. 

Red  spiders  and  mites  of  citrus  trees  are  not  difficult  to  control. 
Neither  is  the  expense  large  as  compared  with  the  control  of  other  pests 
of  citrus  trees.  For  these  reasons,  therefore,  there  is  little  excuse  for 
allowing  such  pests  to  do  injury.  By  the  statement  that  they  are  not 
difficult  to  control  is  meant  that  they  are  susceptible  to  various  sorts  of 
sprays,  some  of  which  may  be  applied  dry.  But  they  do  require  sep- 
arate treatment  where  the  scale  insects  are  handled  by  fumigation,  for 
fumigation  has  practically  no  effect  upon  them.  Where  spiders  and 
mites  alone  are  to  be  combated  the  essential  ingredient  in  the  applica- 
tion should  be  sulphur.  Sulphur  has  the  advantage  over  most  other 
materials  in  that  it  remains  effective  for  some  time  after  the  application 
is  made.  It  is  also  cheap  and  not  hurtful  to  the  tree  or  fruit.  Where 
spraying  is  still  practiced  for  the  control  of  scale  insects,  then  the  oil 
emulsions  may  be  used  for  they  will  control  the  spiders  at  the  same  time. 

FUMIGATION  NOT  EFFECTIVE. 

It  has  been  the  universal  experience  in  actual  practice,  as  well  as  a 
problem  of  easy  determination  experimentally,  that  the  ordinary  dosage 
of  hydrocyanic  acid  gas  used  in  the  fumigation  of  citrus  trees  has  little 
effect  on  spiders  and  mites.  Just  why  they  are  resistant  to  the  gas  can 
not  be  clearly  explained,  but  it  must  be  on  account  of  the  gas  not  being 
able  to  enter  the  spiracles  in  any  quantity.  It  is  scarcely  possible  that 
they  could  resist  any  amount  of  such  gas  if  it  actually  entered  the  body 
tissues.  But  there  are  certain  insects  that  are  almost  resistant  to  arsen- 
ical poisons  though  the  poison  may  actually  occur  in  their  stomachs. 
So  it  is  not  inconceivable  that  the  spiders  are  actually  resistant  to  cer- 
tain amounts  of  gas  as  used  on  citrus  trees,  even  though  such  gas  really 
enters  their  bodies,  but  it  seems  more  likely  that  less  actually  enters 
through  their  breathing  pores  than  is  the  case  with  most  insects. 

The  breathing  or  respiratory  system  is  very  different  in  spiders  and 


520 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


mites  than  it  is  in  insects.  The  silver  mite,  for  instance,  is  said  to  have 
no  tracheal  system  and  no  openings  for  purposes  of  respiration  in  the 
body  surface.  Such  mites  secure  oxygen  through  the  general  body  wall 
by  process  of  osmosis.  In  the  case  of  the  citrus  red  spider  and  the  six- 
spotted  mite  the  spiracles  occur  on  either  side  of  the  rostrum.  There 
are  thus  but  two  while  most  insects  have  several.  This  difference  in  the 
respiratory  system  between  Acarina  and  Insects,  however,  does  not 
explain  all  the  difference  in  resistance  to  the  gas,  for  the  mealy  bug, 
which  is  itself  an  insect,  is  about  as  resistant  as  spiders  and  mites.  But 
in  the  case  of  the  mealy  bug  it  may  be  again  a  question  of  the  gas  not 
actually  getting  through  the  spiracles. 

That  the  citrus  red  spider  is  not  wholly  immune  to  hydrocyanic  acid 
gas  is  shown  in  the  table  below.  The  fumigation  recorded  was  done  in 
an  airtight  box  of  25  cubic  feet  capacity.  Taking  the  dosage  in  field 
work  as  one  ounce  to  100  cubic  feet  of  space,  the  corresponding  amount 
of  potassium  cyanide  to  use  in  the  box  would  be  one  fourth  of  this,  or  7.5 
grams.  It  will  be  noted  that  the  full  dosage  continued  for  one  hour 
failed  to  kill  but  a  small  per  cent  of  the  eggs  of  the  spider.  The  adults 
were  all  killed  with  this  same  dosage,  and  even  down  to  one  half  hour 
exposure.  But  it  should  be  kept  in  mind  that  on  account  of  no  leakage 
this  dosage  is  really  greatly  in  excess  of  that  used  in  actual  fumigation 
work.  With  the  same  dosage  in  the  same  box  we  have  killed  all  stages 
of  the  red,  black  and  purple  scales,  and  even  the  mealy  bug  in  15  minutes 
exposure.  In  fumigation  work,  therefore,  where  the  maximum  dosage  is 
used  a  few  of  the  spiders  may  be  killed,  but  only  a  few  at  best  and  none 
whatever  of  the  eggs. 


Fumigation  for  Red  Spiders. 

Capacity  of  fumigatorium,  25  cubic  feet. 


Materials  used. 

Time  in 
minutes. 

Tem- 
perature. 
F. 

Adults  and  young. 

Exp. 

No. 

gmKCN. 

c.c. 
H2S04. 

c.c.H20. 

Number 
used. 

Number 
killed. 

Per  cent 
killed. 

per  cent 
hatched. 

17 

21 

89 

7.5 

7.5 
7.5 
7.5 
7.5 
7.5 
7.5 
7.5 
7.5 
6.0 
3.0 
4.5 
4.5 
4.0 
4.0 
2.0 
2.0 

7.5            17.7 
7.5            18.7 
7  5            is  v 

60 
60 
30 
30 
15 
15 
15 
10 
5 
10 
60 
60 
60 
60 
60 
60 
60 

60 
65 
68 
68 
65 
67 
69 
75 
70 
67 
74 
70 
70 
70 
65 
80 
61 

147 
584 
235 
274 
310 
345 
321 
169 
224 
202 
188 
229 
222 
286 
224 
264 
296 

147 
584 
235 
274 
260 
342 
321 

100 

100 

100 

100 
83.87 
99.13 

100 

75.71 
82.00 

90 

7.5 
7.5 
7.5 
7.5 
7.5 
7.5 
6.0 
3.0 
4.5 
4.5 
4.0 
4.0 
2.0 
2.0 

18.7 

18.7 

18.7 

18.7 

18.7 

18.7 

15.0 

7.5 

12.0 

12.0 

10.0 

10.0 

5.0 

5.0 

91 

92 

102 

140 

264 

169    !       100 
157            74.55 

265 

190 
171 
229 
222 
253 
224 
256 
246 

94.59 
90.95 

100 

100 
98.95 

100 
96.96 
83.39 

275 

277 

281 

288 

291 

296 

306 

Bulletin  234]         RED    SPIDERS    AND    MITES    OF    CITRUS   TREES. 


521 


LIME  SULPHUR  SPRAY. 

The  spray  that  has  been  found  to  be  most  generally  satisfactory  is  the 
ordinary  commercial  lime  sulphur  spray,  properly  diluted.  There  is  no 
objection  to  the  grower  making  his  own  lime  sulphur  concentrate  if  he 
is  prepared  to  do  so,  but  all  things  considered,  the  commercial  article 
costs  but  little  more  and  is  more  satisfactory.  Most  of  the  lime  sulphur 
sold  in  the  State  is  manufactured  in  the  State  by  two  different  firms,  and 
sold  under  the  trade  names  of  Ortho  and  Rex  lime  sulphur.  These  are 
of  equal  efficiency  when  diluted  in  proportion  to  their  density  or  sulphur 
content  and  are  simply  concentrated  lime  sulphur  solutions.  Where  the 
trade  name  alone  is  used  it  does  not  indicate  that  it  is  some  special  spray 


Fig.  29. — Spraying  large  orange  trees  with  lime  sulphur  for  Red  Spiders. 

of  unknown  composition  but  it  is  simply  lime  sulphur  spray  ready  for 
use  with  the  addition  of  water. 

Dilutions. — During  the  past  year  or  two  the  commercial  lime  sulphur 
has  been  used  at  dilutions  of  1  to  35  and  1  to  50.  So  far  as  we  have 
been  able  to  see  the  1  to  50  dilution  is  as  satisfactory  as  the  1  to  35 
dilution.  If  the  1  to  50  dilution  kills  the  spiders  that  is  all  that  is  neces- 
sary and  there  is  a  considerable  saving  in  the  cost.  The  question  of 
burning  also  comes  in,  and  during  warm  dry  weather  a  considerable 
amount  of  this  may  occur  with  the  1  to  35  strength.  The  injury  from 
lime  sulphur  is  evident  as  brown  spots  on  the  tips  or  margins  of  the 


522 


UNIVERSITY    OF   CALIFORNIA EXPERIMENT    STATION. 


leaves.    The  spray  has  collected  here  and  by  the  evaporation  of  the  water 
it  becomes  much  more  concentrated  and  causes  such  local  burning. 

The  dilution  of  one  gallon  of  the  concentrate  to  fifty  gallons  of  water 
is  intended  for  the  36°  material.  That  is,  the  product  in  the  barrel  as 
it  comes  from  the  manufacturer  should  read  36°  on  the  Baume  scale. 
If  it  is  not  so  concentrated  as  this  then  the  dilution  should  not  be  so 
great.  Sometimes  the  grower  dilutes  according  to  the  specific  gravity 
spindle  and  the  reading  on  this  to  correspond  to  the  1  to  50  dilution 
should  be  1.0065  or,  if  the  Baume  scale  is  used  it  should  indicate 
about  1°. 

Cost. — Where  the  grower  hires  the  work  done  the  total  cost,  including 
the  materials  and  the  application,  varies  from  1J  to  2\  cents  a  gallon  as 
it  is  applied  to  the  tree.  The  usual  charge  is  \\  cents  where  the  dilution 
is  1  to  50  and  2  cents  where  the  dilution  is  1  to  35.  In  some  cases, 
however,  2 \  cents  is  charged  for  the  latter  dilution. 


Fig.  30. — Spraying  young  orange  trees  for  Red  Spiders. 

What  the  Spray  Does. — The  lime  sulphur  spray  kills  the  spiders 
largely  by  contact.  It  is,  therefore,  important  that  the  spray  be 
thoroughly  applied  in  order  to  reach  all  of  the  spiders.  Fortunately 
the  spiders  are  found  mostly  on  the  outer  parts  of  the  tree,  and  the 
usual  difficulty  of  getting  to  the  interior  of  the  citrus  tree  with  the  spray 
is  not  important  in  this  case.  From  our  experiments  and  observations 
the  lime  sulphur  spray  does  not  kill  all  of  the  eggs  of  the  spider,  even 
though  these  be  hit  with  the  spray.  It  does,  however,  kill  a  large 
proportion  of  them.  But  the  lime  sulphur  spray  is  not  dependent  on 
its  efficiency  entirely  through  contact.  Its  effect  is  more  or  less  lasting, 
and  consequently  the  young  which  may  hatch  from  those  eggs  not  killed 
will  succumb  usually  soon  after.  Evidence  of  the  spray  may  be  seen 
several  weeks  after  the  application  is  made.     In  some  cases,  as  with  the 


Bulletin  234] 


RED    SPIDERS    AND    MITES    OF    CITRUS   TREES. 


523 


spiders  on  hops  and  almonds  in  the  northern  part  of  the  State,  a  flour 
paste  is  added  to  increase  adhesiveness.  But  the  addition  of  anything 
extra  to  the  straight  lime  sulphur  spray  seems  to  be  superfluous  in  the 
case  of  the  citrus  spiders. 


Fig.  31. — Orange  leaves  sprayed  with  lime  sulphur. 

DRY  SULPHUR. 

The  earliest  successful  treatment  for  spiders  or  mites  was  sulphur 
applied  dry  or  simply  dusted  over  the  plants.  This  still  remains  one 
of  the  most  satisfactory  remedies.  But  satisfactory  results  are  more 
dependent  upon  the  weather  than  is  the  case  with  the  spray.  By  proper 
weather  conditions  is  meant  nights  with  more  or  less  moisture,  and  days 
of  bright  sunshine,  with  a  temperature  high  enough  to  properly  act  upon 
the  sulphur.  This  temperature  is  roughly  about  75°  F.  or  above  in  the 
shade.  Such  weather  conditions  generally  prevail  in  the  southern  Cali- 
fornia citrus  belt  during  the  spring  when  the  spiders  are  most  numerous. 

How  the  Sulphur  Acts.— The  exact  manner  in  which  dry  sulphur  acts 
upon  the  spiders  is  still  obscure.  That  is,  it  is  not  known  whether  the 
fumes  given  off  are  sulphurous  acid  gas,  hydrogen  sulfid,  or  simply  the 
vapors  of  sulphur.  But  whatever  be  the  nature  of  the  actual  killing 
substance,  from  a  practical  standpoint  the  range  through  which  this 
killing  material  acts  is  most  important.  This  range  we  have  determined 
by  experiment  to  be  exceedingly  short.  A  thin  thread  of  tanglefoot  was 
made  to  enclose  an  area  containing  spiders  in  all  stages  on  the  fruit  of 
the  lemon.  Another  area  immediately  adjoining,  separated  only  by  the 
thread  of  tanglefoot,  also  enclosed  spiders.  In  the  first  area  sulphur 
was  thoroughly  dusted  while  no  sulphur  was  applied  to  the  other  area. 
After  a  day  or  two  all  the  spiders  were  killed  in  the  sulphured  area 


524 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


while  those  in  the  other  cell  were  unharmed.  Here,  then,  the  thickness 
of  the  strip  of  tanglefoot,  which  was  no  greater  than  No.  10  thread,  was 
sufficient  to  prevent  the  sulphur  from  acting  on  the  spiders.  This  was 
repeated  several  times  with  the  same  result. 

How  Applied.— The  practical  lesson  to  be  heeded  from  the  above 
experiment  is  that  the  sulphur  must  be  thoroughly  and  evenly  applied. 
There  are  many  growers  who  still  believe  that  throwing  quantities  of 
sulphur  on  the  ground  or  putting  handfuls  in  the  crotches  of  the  tree  is 
sufficient  to  check  the  spiders.     If  the  spiders  disappear  under  such  con- 


Fig.  32. — Mixing  the  sulphur  and  the  hydrated  lime. 

ditions  and  by  coincidence  they  often  do,  and  thus  the  method  gains 
credence,  it  is  apart  from  any  influence  the  sulphur  may  have. 

If  a  spray  is  to  be  applied  a  successful  grower  will  first  secure  an  outfit 
that  will  properly  apply  the  material.  If  dry  sulphur  is  to  be  applied, 
many  still  adhere  to  the  old-fashioned,  wasteful  and  inefficient  method  of 
applying  it  by  hand.  Applications  made  in  such  a  manner  should  not  be 
expected  to  give  satisfactory  results.  For  large  trees  it  is  necessary  to 
have  a  dust  blower  made  for  the  purpose  with  a  gasoline  engine  for  the 
power.  Such  a  machine  is  shown  in  Figs.  33  and  34.  For  small  trees  a 
hand  rotary  bellows  as  shown  in  Fig.  35  is  very  satisfactory,  or  in  the 
grape  sections  the  Vermorel  machine  may  be  used. 

When  the  Application  Should  he  Made. — The  season  for  applying 
sulphur  or  the  sulphur  spray  is  when  the  spiders  first  become  numerous 
and  the  tree  begins  to  show  indications  of  injury.     This  is  usually  in  the 


Bulletin  234]         RED    SPIr)ERS   AND   MITES    OF    CITRUS   TREES. 


525 


Fig.   33. — Side  view  of  power  dusting  machine  for  applying  dry  sulphur  and 

hydrated  lime. 


Fig.  34. — Applying  dry  sulphur  and  hydrated  lime  for  Red  Spiders. 


526 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


spring  or  early  summer,  but  sometimes  treatment  is  required  at  other 
seasons,  as  the  fall  or  winter.  As  stated  in  the  introduction,  it  is  not 
good  economy  to  apply  treatment  unless  the  spiders  are  abundant 
enough  to  warrant  expenditure  of  the  money  required,  which  should 
be  a  saving  over  the  injury  that  would  be  done  by  the  spiders.  On  this 
basis  some  groves  will  require  treatment  while  others  immediately 
adjoining  may  not. 

As  to  the  time  during  the  twenty-four  hours,  the  application  should 
be  made  very  early  in  the  morning  or  during  the  whole  of  the  night. 
Experience  in  the  Whittier  section  during  the  past  year,  where  the  work 


Fig. 


35. — Applying   dry   sulphur   to   small   citrus   trees  by   means   of   a   hand 
dusting  machine. 


has  been  done  at  night,  indicates  strongly  the  advantage  of  this  time 
over  that  of  the  day.  First,  there  is  no  wind,  or  at  least  much  less  than 
during  the  day ;  second,  the  moisture  is  sufficient  to  insure  the  sulphur 
adhering  to  the  foliage.  Evidence  of  sulphur  has  been  noted  even 
months  after  the  application  was  made ;  third,  aside  from  the  moisture 
on  the  tree  itself,  the  humidity  of  the  atmosphere  keeps  the  sulphur  in  a 
more  definite  cloud  about  the  tree,  and  thus  insures  more  settling  on  the 
tree,  and,  fourth,  application  made  at  night  is  much  more  satisfactory 
to  the  men.  They  can  better  avoid  the  cloud  of  sulphur,  and  the  com- 
bination of  the  sulphur  and  the  bright  hot  sun,  which  is  so  disagreeable, 
is  avoided. 


Bulletin  234]         RED   SPIDEKS   ANr)   MITES   OF   CITRUS   TREES.  527 

Materials. — Sulphur  is  no  longer  applied  alone,  under  the  best  prac- 
tice. While  it  is  still  the  essential  ingredient,  it  has  been  found  that  the 
addition  of  an  adhesive  material  adds  greatly  to  its  efficiency.  This 
material  is  hydrated  lime.  Hydrated  lime  not  only  serves  to  cement  the 
sulphur  to  the  foliage,  but  also  acts  as  a  carrier  and  a  dilutent. 
Hydrated  lime,  which  is  a  fine,  dry  powder,  is  formed  by  the  addition  of 
water  in  the  right  proportion  to  quicklime.  It  is  thus  still  caustic  but 
not  so  caustic  as  quicklime,  so  that,  as  to  properties,  it  may  be  said  to 
occupy  a  position  between  air  slaked  and  quick  lime.  Hydrated  lime 
can  be  obtained  in  the  market  at  a  small  cost.  Or  it  may  be  made  at 
home  by  adding  32  pounds  of  water  to  100  pounds  of  the  quicklime,  the 
32  pounds  of  water  being  taken  up  during  the  process  of  hydration. 
The  precaution  to  be  observed  in  its  making  is  not  to  add  too  much  water. 
If  too  much  is  used,  more  quicklime  may  be  added. 

As  to  sulphur,  the  important  requisite  is  fineness.  The  same  weight 
of  sulphur  will  go  further,  can  be  better  applied,  and  adheres  to  the  tree 
better  if  it  is  in  a  finely  divided  condition.  A  finely  divided  sublimed  or 
powdered  sulphur  is,  therefore,  to  be  preferred.  The  proportion  of  sul- 
phur to  hydrated  lime  varies  in  actual  use,  but  the  usual  proportion  is 
three  parts  sulphur  to  one  of  the  lime.  A  box  five  or  six  feet  square  and 
a  foot  deep,  as  shown  in  Fig.  32,  may  be  used  for  the  mixing.  Three 
sacks  of  sulphur  to  one  of  hydrated  lime  are  put  in  this  box  and  the  mix- 
ing done  by  means  of  a  large  hoe.  It  is  then  ready  to  be  placed  in  the 
hopper  of  the  dust  machine  and  applied  to  the  tree. 

Dry  Sulphuring  and  the  Fruit  Pickers. — Where  the  harvesting  of  the 
fruit  occurs  a  few  days  after  the  dry  sulphur  has  been  applied  there  is 
much  complaint  from  the  pickers  about  the  disagreeableness  of  work- 
ing in  the  sulphur.  The  schedule  of  sulphuring  should,  therefore,  be 
arranged  to  follow  the  picking,  in  the  case  of  lemons,  as  soon  as  possible, 
in  order  for  sufficient  time  to  elapse  before  the  next  picking.  The  sul- 
phuring should  also  consider  the  time  of  harvesting  the  Valencia  orange, 
since  picking  may  occur  at  a  time  when  the  spiders  are  numerous.  Sul- 
phuring very  rarely  interferes  with  the  harvesting  of  the  Navel  orange. 
The  effects  of  the  dry  sulphur  are  noticeable  to  the  pickers  sometimes  for 
two  or  three  weeks  afterward,  but  it  should  not  warrant  serious  com- 
plaint at  this  time  or  a  change  in  practice. 

THE  DRY  VERSUS  THE  LIQUID  SPRAY. 

The  liquid  application  of  sprays  is  more  generally  practiced  and  more 
universally  satisfactory  than  the  dry  or  dust  applications,  with  a  few 
exceptions.  Dry  sulphur  is  more  effective  than  the  liquid  for  the  con- 
trol of  the  Oidium  of  the  vine.  A  spray  will  kill  only  the  fungus  that 
is  struck  by  the  spray,  and  it  is  almost  impossible  to  reach  every  par- 
4—234 


528  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

tide  of  the  vine.  The  dust  on  the  other  hand  is  blown  into  the  vine  as  a 
cloud  and  the  whole  atmosphere  is  charged  with  sulphur  and  all  parts  of 
the  plant  come  in  contact  with  it.  The  same  thing  is  largely  true  of  the 
red  spider  on  citrus.  The  spray,  however,  appears  to  kill  more  than  is 
actually  hit,  and  the  deposit  of  sulphur  formed  on  the  leaf  continues 
effective  for  some  time.  But  the  amount  of  sulphur  is  less,  and  often- 
times less  evenly  distributed,  than  is  the  case  with  the  dry  application. 
The  dry  sulphur  does  not  kill  so  quickly  and  two  or  three  days  to  a  week 
are  necessary,  depending  on  the  weather  conditions.  But  it  will  con- 
tinue to  act  in  some  cases  for  two  or  three  weeks  afterward.  The  fact 
that  in  the  Whittier  section  this  year  pickers  have  complained  of  the 
sulphur  three  weeks  after  it  was  applied  is  evidence  that  it  is  still  there 
and  active. 

The  dry  sulphur  is  more  easily  and  quickly  applied  but  it  is  more  dis- 
agreeable to  apply.  This  effect  also  lasts  more  or  less  in  the  cultivation 
and  other  work  in  the  grove,  including  the  picking,  as  already  explained. 
Some  prefer  to  spray  because  they  already  have  a  spraying  outfit,  and  it 
obviates  the  necessity  of  purchasing  additional  equipment.  If  the 
grower  is  to  buy  an  outfit  then  the  dust  blower  will  cost  less.  Others 
spray  because  the  lime  sulphur  is  supposed  to  be  efficient  for  the  control 
of  other  troubles,  as  fungous  diseases.  But  there  is  no  evidence  to  show 
that  the  dry  application  may  not  also  be  effective  against  such  troubles. 
Some  prefer  to  spray  because  they  are  interested  or  have  been  made  to 
become  interested  in  the  spray  material.  If  the  weather  conditions  are 
not  satisfactory  poor  results  may  be  expected  from  the  dry  application, 
while  with  the  same  weather  conditions  the  spray  will  give  satisfactory 
results.  This  is  dependent,  however,  on  how  thoroughly  the  spraying  is 
done.  For,  with  cold  weather,  the  spray  will  kill  all  of  the  spiders  it 
hits,  but  it  will  not  kill  all  of  the  eggs,  and  the  young  hatching  from 
these  will  not  be  killed  by  the  deposit  remaining  from  the  spray. 

The  question  of  whether  the  wet  or  the  dry  spray  is  the  more  desirable 
is,  therefore,  a  question  largely  of  cost.  There  is  no  doubt  that  an  appli- 
cation of  dry  sulphur  made  during  the  spring  or  early  summer  when  the 
spiders  are  usually  most  abundant  will  control  them.  The  lime  sulphur 
spray  will  also  control  them,  and  the  spray  has  some  advantages  over  the 
dry  or  dust  method.  The  cost  of  the  spray  is  from  1^  to  2\  cents  a 
gallon  as  applied  to  the  tree.  The  number  of  gallons  required  varies 
according  to  the  size  of  the  trees,  but  the  average  will  be  from  eight  to 
ten  gallons  per  tree.  On  this  basis  the  cost  for  spraying  will  be  from  12 
to  25  cents  with  an  average  of  15  to  18  cents.     As  compared  with  this 


Bulletin  234]         RED    gPIDEBS     \\l>    KITES    OF    CITRUS   TREES.  521) 

the  dry  sulphur  will  cost  from  7  to  9  .cents  a  tree.     This  cost  is  cal- 
culated, from  an  average  grove,  as  follows : 

Cost  of  machine,  labor  and  teams  5$  days,  at  $15.00 $82.50 

3520  pounds  sulphur  at  .02f 97.80 

1100  pounds  hydrated  lime,  at  .01 11.00 

Total  cost $191.30 

Cost  per  acre $8.70 

Cost  per  tree .087 

Amount  of  sulphur  per  acre 160  pounds 

Amount  of  lime  per  acre 50  pounds 

The  expense  of  applying  the  liquid  spray  will  be  approximately  twice 
that  of  the  dry  or  dust  spray.  The  above  figures  represent  the  cost 
where  the  work  and  machine  are  hired  done.  The  cost  would  be  much 
less  where  the  grower  has  his  own  outfit. 

DISTILLATE  OR  KEROSENE  EMULSION. 

It  often  happens  that  the  black  or  other  scales  may  be  desired  to  be 
controlled  along  with  the  spiders.  Dry  sulphur  or  the  sulphur  spray  is 
of  no  use  whatever  against  these.  In  such  cases  the  distillate  or  kero- 
sene (water- white  oil)  emulsion  is  most  effective.  Indeed  the  distillate 
emulsion  has  given  good  results,  with  two  or  three  applications,  with 
such  a  resistant  insect  as  the  mealy  bug.  Spraying  is  not  expected  to 
replace  fumigation,  but  fumigation  has  no  effect  on  the  spiders  and  little 
effect  on  the  mealy  bug  unless  excessive  dosages  are  used,  or  two  or 
three  applications  made.  Two  or  three  applications  of  a  spray  seem 
to  be  the  most  desirable  method,  at  the  present  time,  of  handling  the 
mealy  bug.  If  spiders  occur  where  this  insect  is  present,  therefore,  a 
spray  that  will  control  both  pests  at  the  same  time  is  the  most  practicable. 

It  may  happen,  too,  that  trees,  particularly  small  trees,  infested  with 
the  black  scale,  or  even  the  red  scale,  and  the  red  spider,  may  be  given 
one  treatment  for  both  pests.  Where  fumigation  fails  to  control  such  a 
pest  as  the  mealy  bug,  even  though  the  trees  and  fruit  be  severely 
burned,  then  it  is  just  as  well  to  use  a  spray. 

The  injury  to  the  trees  caused  by  the  old  distillate  spray  is  now  largely 
avoided  by  the  higher  gravity  oil,  and  making  a  good  stable  emulsion  by 
the  addition  of  soap.  A  certain  per  cent  of  oil  in  a  mechanical  mixture 
may  injure  the  tree,  but  the  same  per  cent  of  oil  made  into  a  stable 
emulsion  has  no  injurious  effect  upon  the  tree. 

The  results  from  spraying  are  dependent  entirely  on  the  men  behind 
the  nozzles,  if  the  spray  materia]  used  is  known  to  kill  such  as  are  hit. 
The  citrus  tree  presents  unusual  difficulties,  on  account  of  its  dense  foli- 
age, for  covering  all  of  its  surface.  A  very  small  part  of  the  tree  can  be 
covered  from  one  position  of  the  nozzle.  It  is  thus  necessary  to  strike 
the  tree  from  every  possible  angle  with  a  pressure  of  about  200  pounds. 


530  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

The  formula  for  the  distillate  emulsion  is  as  follows : 

Distillate  32°  to  34°  Beaume 4  gallons 

Whale  oil  soap 10  pounds 

Water   200  gallons 

Put  15  or  20  gallons  of  hot  water  in  the  spray  tank  and  add  the  soap 
with  the  agitator  going.  When  the  soap  is  thoroughly  dissolved  add  the 
oil  slowly,  the  agitator  going  at  full  speed  in  the  mean  time.  After  the 
oil  is  added  and  thoroughly  agitated  dilute  to  200  gallons  with  cold 
water.. 

Other  Sprays. 

During  the  course  of  the  investigation  of  red  spiders  several  other 
sprays  have  been  tried,  both  home  made  and  commercial  compounds  but 
it  is  unnecessary  to  discuss  any  more  than  those  already  given. 

SUMMARY. 

Red  spiders  and  mites  do  considerable  injury  to  citrus  trees  in  south- 
ern California  each  year.  Their  numbers  vary  greatly  even  in  adjoin- 
ing groves  and  treatment  is  unnecessary  unless  they  are  abundant  and 
doing  damage. 

The  citrus  red  spider  is  the  most  destructive  of  all  the  species  and  is 
the  one  most  widely  distributed. 

The  next  most  important  species  is  the  six-spotted  mite,  which  makes 
conspicuous  light-colored  areas  on  the  leaves. 

Red  spiders  and  mites  live  and  breed  entirely  on  the  trees  and  are 
only  incidentally  found  on  the  ground. 

About  30  eggs  are  laid  by  each  female  and  from  eight  to  twelve  days 
are  necessary  to  bring  them  to  maturity. 

There  are  thus  several  generations  in  a  year,  varying  from  12  to  15. 

They  are  most  abundant  usually  during  May  and  June,  but  some- 
times become  numerous  at  other  seasons. 

Aside  from  the  two  or  three  of  the  most  injurious  species  we  have 
recorded  several  others  in  these  studies,  making  a  total  of  14. 

The  natural  enemies  attacking  spiders  and  mites  are  varied  and  num- 
erous.    The  biology  of  many  of  these  is  given  for  the  first  time. 

The  most  effective  control  measures  are  the  application  of  dry  sulphur 
and  hydrated  lime,  or  the  commercial  lime  sulphur  spray. 


REPORTS. 

1896.  Report  of  the  Viticultural  Work  during  the  seasons  1887-93,  with  data  regard- 

ing the  Vintages  of  1894-95. 

1897.  Resistent  Vines,  their  Selection,  Adaptation,  and  Grafting.     Appendix  to  Viti- 

cultural Report  for  1896. 

1902.  Report  of  the  Agricultural  Experiment  Station  for  1898-1901. 

1903.  Report  of  the  Agricultural  Experiment  Station  for  1901-03. 

1904.  Twenty-second  Report  of  the  Agricultural  Experiment  Station  for  1903-04. 

BULLETINS. 


Reprint. 
No.  12S. 

133. 

147. 

162. 

164. 

167. 

168. 

169. 

170. 
171. 

174. 
176. 


177. 


178. 
179. 


181. 
182. 


183. 
184. 


185. 


186. 
187. 


189. 

191. 
192. 

194. 

195. 

197. 


Endurance  of  Drought  in  Soils 
of  the  Arid  Regions. 

Nature,  Value,  and  Utilization  of 
Alkali  Lands,  and  Tolerance 
of  Alkali.  (Revised  and  Re- 
printed, 1905.) 

Tolerance  of  Alkali  by  Various 
Cutures. 

Culture  Work  of  the  Sub-sta- 
tions. 

Commercial  Fertilizers.  (Dec. 
1,    1904.) 

Poultry  Feeding  and  Proprie- 
tary Foods. 

Manufacture  of  Dry  Wines  in 
Hot  Countries. 

Observations  on  Some  Vine 
Diseases  in  Sonoma  County. 

Tolerance  of  the  Sugar  Beet  for 
Alkali. 

Studies  in  Grasshopper  Control. 

Commercial  Fertilizers.  (June 
30,    1905.) 

A  New  Wine-cooling  Machine. 

Sugar  Beets  in  the  San  Joaquin 
Valley. 

A  New  Method  of  Making  Dry 
Red  Wine. 

Mosquito  Control. 

Commercial  Fertilizers.  (June, 
1906.) 

The  Selection  of  Seed-Wheat. 

Analyses  of  Paris  Green  and 
Lead  Arsenate.  Proposed  In- 
secticide Law. 

The  California  Tussock-moth. 

Report  of  the  Plant  Pathologist 
to  July  1,  1906. 

Report  of  Progress  in  Cereal 
Investigations. 

The  Oidium  of  the  Vine. 

Commercial  Fertilizers.  (Janu- 
ary, 1907.) 

Lining  of  Ditches  and  Reser- 
voirs to  Prevent  Seepage 
Losses. 

Commercial  Fertilizers.  (June, 
1907.) 

California  Peach  Blight. 

Insects  Injurious  to  the  Vine  in 
California. 

Commercial  Fertilizers.  (Dec, 
1907.) 

The  California  Grape  Root- 
worm. 

Grape  Culture  in  California ; 
Improved  Methods  of  Wine- 
making  ;  Yeast  from  California 
Grapes. 


No.  198.     The  Grape  Leaf -Hopper. 
199.     Bovine  Tuberculosis. 

201.  Commercial  Fertilizers.      (June, 

1908.) 

202.  Commercial     Fertilizers.        (De- 

cember,   1908.) 

203.  Report  of  the  Plant  Pathologist 

to  July  1,   1909. 

204.  The    Dairy    Cow's    Record    and 

the  Stable. 

205.  Commercial     Fertilizers.        (De- 

cember,   1909.) 

206.  Commercial    Fertilizers.     (June, 

1910.) 

207.  The    Control    of    the    Argentine 

Ant. 

208.  The  Late  Blight  of  Celery. 

209.  The  Cream  Supply. 

210.  Imperial    Valley    Settlers'    Crop 

Manual. 

211.  How   to    Increase    the    Yield   of 

Wheat  in  California. 

212.  California  White  Wheats. 

213.  The  Principles  of  Wine-making. 

214.  Citrus  Fruit  Insects. 

215.  The  Housefly  in  its  Relation  to 

Public  Health. 

216.  A    Progress    Report    upon    Soil 

and  Climatic  Factors  Influenc- 
ing the  Composition  of  Wheat. 

217.  Honey  Plants  of  California. 

218.  California  Plant  Diseases. 

219.  Report  of  Live  Stock  Conditions 

in  Imperial  County,  California. 

220.  Fumigation  Studies  No.  5  ;  Dos- 

age Tables. 

221.  Commercial  Fertilizers.  October, 

1911.) 

222.  The  Red  or  Orange  Scale. 

223.  The  Black  Scale. 

224.  The    Production    of     the    Lima 

Bean. 

225.  Tolerance     of     Eucalyptus     for 

Alkali. 

226.  The  Purple  Scale. 

227.  Grape  Vinegar. 

228.  Pear    Thrips    and    Peach    Tree 

Borer. 

229.  Hog     Cholera     and     Preventive 

Serum. 

230.  Enological  Investigations. 

231.  Walnut    Culture    in    California. 

Walnut  Blight. 

232.  Commercial  Fertilizers. 

233.  Three  Years'  Work  of  the  Fern- 

dale   (Humboldt  County)   Cow 
Testing  Associations. 


CIRCULARS. 


No. 


10, 


11. 

29. 


46. 


52. 


55. 

CO. 

81. 


Texas  Fever. 

Remedies  for  Insects. 

Asparagus  Rust. 

Reading  Course  in  Economic 
Entomology. 

Fumigation  Practice. 

Preliminary  Announcement  Con- 
cerning Instruction  in  Practi- 
cal Agriculture  upon  the  Uni- 
versity Farm,  Davis,  Cal. 

Instruction  in  Practical  Agricul- 
ture at  the  University  Farm. 

Suggestions  for  Garden  Work  in 
California  Schools. 

Information  for  Students  Con- 
cerning the  College  of  Agricul- 
ture. 

Farmers'  Institute  and  Univer- 
sity Extension  in  Agriculture. 

Butter  Scoring  Contest,   1910. 

University  Farm  School. 


No.     62.     The      School      Garden      in      the 
Course  of  Study. 
63.     How    to    Make   an   Observation 
Hive. 

65.  The  California  Insecticide  Law. 

66.  Insecticides  and  Insect  Control. 

67.  Development        of        Secondary 

School     Agriculture     in     Cali- 
fornia. 

68.  The  Prevention  of  Hog  Cholera. 

69.  The  Extermination  of  Morning- 

Glory. 

70.  Observation    of    the     Status    of 

Corn  Growing  in  California. 

74.  Rice. 

75.  A  New  Leakage  Gauge. 

76.  Hot  Room  Callusing. 

77.  University  Farm  School. 

78.  Announcement        of        Farmers' 

Short  Courses  for  1912. 

79.  List  of  Insecticide  Dealers. 


f 


